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Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS BOOTCAMP
Todd Bacastow
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Geography matters!
• ‘Geographic Information’ is information which can be related to specific locations.
• Most human activity depends on geographic information.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Topic 1: What is GIS?
• Dozens of possible definitionsSome emphasise the technology
The Hardware The Software
Others focus on applications Other terms often encountered: LIS,
AM/FM, Geo-information systems, etc. May emphasise different roles for the
system, e.g. spatial decision support system, spatial database system, etc.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
One definition of GIS (Dueker and Kjerne,
1989)
• “Geographic Information Systems - A system of hardware, software, data, people, organizations and institutional arrangements for collecting, storing, analysing, and disseminating information about areas of the Earth”
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Geographic Information System
• Concepts such as location, direction, distance, proximity, adjacency provide links between different data Geographic information usually broken down
into three linked components of Space Time Attribute
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Geographic Information System
• An Information System is a set of processes, executed on raw data, to produce information which will be useful in decision-making
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Geographic Information System
• In a system the whole is greater than the sum of its parts (Aristotle, C4th BC)
GIS is a convergence of technological fields and traditional disciplines
Not just technology: the data, people and institutional context are as much part of GIS as are the computers and software
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS is the convergence of many disciplines:
• Geography
• Cartography
• Remote Sensing
• Photogrammetry
• Surveying
• Geodesy
• Statistics
• Operations Research
• Computer Science
• Mathematics
• Civil Engineering
• Business management
• Behavioural science
• Etc….
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS as a tool
• Majority view of GIS
• Focus is on hardware, software and routines
• A technocentric perspective
• The favoured viewpoint of the system vendors
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS as science
• Emphasis is on data, human uses, contexts
• A more academic perspective
• Geographic information science is the “science behind the systems”
• Includes concepts of spatial reasoning, cognition, human-machine communication, visualisation, data modelling, etc.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS is a product of a particular culture
• Most GIS developed in Europe/N. AmericaUSA: Arc/Info, ArcView, Intergraph,
Bentley, Autodesk, MAP, GRASS... Canada: Caris, Spans, GeoVision...France: GeoConcept, Carto 2-D...UK: Smallworld, GIMMS, Laserscan...Netherlands: ILWIS, PC Raster...
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
GIS is a commercial product
• Developments often driven by commercial considerations, less by scientific ones
• Vendor’s decisions usually based on questions of profitability
• Critical evaluation of proprietary GIS is rare
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Boundaries of GIS are being pushed back
• GIS techniques and concepts increasingly seen in other areas and applications:“Office” type softwareIn-car navigation and other route-
finding systemsMultimedia presentationsThe InternetWAP, SMS, & MMS phone technology
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
What GIS is not
• GIS is not simply the technology: it also has a (growing and important) conceptual base
• GIS can not produce good results from bad data or poor conceptual frameworks
• GIS is not simply a program to produce maps
• GIS is not a substitute for thinking! • GIS is not the universal answer to all
problems!
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Topic 2: Sources of Spatial Data
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Data input - a major bottleneck
• Costs of input often >80% of project costs
• Labor intensive, tedious, error-prone
• Construction of the database may become an end in itself the project may not move on to
analysis of the data collected• Essential to find ways to reduce
costs, maximise accuracy
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Manual data conversion involves three stages
• State 1: GeocodingThe conversion of analogue maps to
digital form
• Stage 2: Entering attribute valuese.g. the heights to associate with
digitised contour lines
• State 3: Linking attribute data to their own geocoded features
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Digital map data: three possible situations.
• The data we want already existHopefully we can find and buy them
(or they may even be free!)
• Data exist but not in digital formWill require conversion from
analogue format
• Data do not exist at allWill need to collect the data
ourselves by remote sensing, field data collection, etc.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Data exist in digital form
•To be useful, have to be in right format, resolution, etc.
•Metadata can inform us as to fitness for purposeunfortunately such information
not always availablemay lead to misinterpretation,
false expectations about accuracy
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Sources of digital map data
• National Mapping Organization
• Other government agencies
• Commercial data vendors
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Standards
•standards may be set to assure uniformity within a
single data set or across several data sets
ensure the data can be shared across different hardware and software platforms
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Some popular standards for digital
map data include• For Vector
data DXF and DWG NTF DLG TIGER SDTF DIGEST .E00 (Arc
Export) format Shapefiles
• For Raster dataBILBSQDEMTIFF JPEGBMP
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Data exist but not in digital form
• Need tools to convert analogue maps or other source documents to digital format
• Digitizing may be performed manually or through automation Manual methods tedious & error
prone Automated techniques may create
bigger editing problems later
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
What if the Data do not exist at all?
• Field data captureMay be done manually (e.g. direct
survey), automatically (e.g. automatic data loggers, etc.) or a combination of the two
• Remote sensingIncludes satellite imagery,
geophysical survey, air photosMay be used as alternative source of
data
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Criteria for choosing modes of input
• Type of data sourceimages favour scanningmaps can be scanned or digitised
• Database model of the GISscanning easier for raster, digitising
for vector• Density of data
dense linework makes for difficult digitizing
• Expected applications of the GIS implementation
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Integrating different data sources: issues
• Formatsmany different format standards exist a good GIS can accept and generate
datasets in a wide range of standard formats
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Integrating different data sources: issues
• Projections Many ways exist to represent curved surface
of the earth on a flat map Some projections are very common A good GIS can convert data from one
projection to another, or to latitude/longitude Input derived from maps by scanning or
digitizing retains the original map's projection
With data from different sources, a GIS database often contains information in more than one projection, and must use conversion routines if data are to be integrated or compared
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Integrating different data sources: issues
• Scaledata may be input at a variety of
scalesscale is an important indicator of
accuracymaps of the same area at different
scales will often show the same features
variation in scales can be a major problem in integrating data
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Integrating different data sources: issues
• Resampling rastersRaster data from different sources
may use different pixel sizes, orientations, positions, projections
Resampling is the process of interpolating information from one set of pixels to another
Resampling to larger pixels is comparatively safe, resampling to smaller pixels is very dangerous
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Topic 3: Representing Spatial Entities
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Representing Spatial Entities
• The object-focused approachBased on recognition of discrete
objects or entitiesMay be layer-based or object-
orientedUsually represented by Vector GIS
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Two ways of representing space in a GIS
• The Tesseral (field-oriented) approachTypically seen in Raster GISAlso in some other models
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Vector data models
• Based on the recognition of discrete objects or entities
• The location/boundaries of these objects defined with respect to some coordinate system
• Emphasis is on boundaries, space within and between boundaries implied
• Objects are usually defined in terms of points, lines and areas
• Complex graphic objects are seen as amalgamations of simpler ones
• Typical Vector GIS include ARC/INFO, MapInfo Intergraph MGE
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Separation of Locational and Attribute data
• In vector GIS, geographic information is represented in terms ofLocational / geometric data
(“where?”)Attribute information (“what?”)Relationships between objects and
attributes
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The vector data model
• Fundamental spatial primitive is a pointDefined by a single x,y coordinate
pair
• Points can be used to locate spatial objectsrepresent Vertices (single = “vertex”)
defining a linerepresent Nodes defining start- or
end-points on lines, junctions where lines meet, etc.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The vector data model
• Sequences of points can be used to define lines
• Lines themselves can be aggregated to represent Networks Boundaries of polygons and regionsTopographic features (contours,
breaks of slope, etc.).
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Topology
• An essential element of vector GIS
• A distinct branch of mathematics
• Defines spatial relationships between objectsAdjacency, connectivity,
containment, etc.
• Essential for most vector GIS operations
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Advantages and disadvantages of the vector
approach• Lower data volumes
• More adaptable to variations in scale/resolution of phenomena
• Tends to be more suited to social and economic applications
• Disadvantages: Less adaptable to uncertainty, fuzziness Often no “lowest common denominator” of
aerial unit .
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Objects versus layers
• Major point of discussion in GIS since mid-1980s
• Alternative strategies for vector representation of geographic space a “stacked” sequence of layers a collection of discrete objects
• Difference in how contents of the database represents the real world
• Echoes wider developments in Computer Science
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The Object view
• More closely mirrors natural ways of seeing the world
• Objects usually used in speaking, writing, thinking about the world
• Objects are fundamental to our understanding of geography
• Object-oriented approaches may offer data storage and processing advantages
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
What are these objects?
• Graphics objects can be points, lines, areas
• Geographic objects can be roads, houses, hills, etc.
• A space can be occupied by many, or no, objects A river is an object (has an identity, name,
coordinates, properties, etc.) A line is an object (also has an identity,
name, coordinates, properties, etc.)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Applications of object view:
• Utilities and facilities managementConcept of empty space littered with objects
fits many needs of managing infrastructureTwo or more objects may occupy same
horizontal position, separated verticallySmaller objects may be part of larger ones
(e.g. pipes as part of networks) and vice versa
Idea of a variable measured everywhere on Earth has little relevance
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The Layer view
• Locations specified by a system of coordinates
• Geography of real world conceptualised as a series of variables (soils, land use, elevation, etc.)
• Each layer in the database represents a particular variable
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The Layer view
• Layer view often more compatible with theories of atmospheric, ocean processes
• Object view is less compatible with concept of continuous change
• Good for resource management applications
• Much data for environmental modelling derived from remote sensing Implies a layer view
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Disadvantages
• The layer approach usually requires many different files to represent each layer
• Some files contain the actual data
• Some contain registration information
• Some contain topological information to construct complex geometries from more primitive ones
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Applications of layer view
• Resource managementgeographic variation can be
described by relatively small amount of variables
conceptualisation reasonably constant between scales
movement of individuals can lead to difficulties of representation and tracking across layers
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Tesseral approaches to GIS
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Tesseral geometries
• From the Greek, tetara or Latin tessella = a tile
• Tessallations are “sets of connected discrete two-dimensional units” thus mosaics or tilings of space
• May be regular or irregular
• Focus is on space occupancy
• Emphasis is on areas, boundaries are implied
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Conceptual basis: creating a tessallation
• Define a geographic area of interest
• Undertake sampling of the entire area
• Each point is space is assigned a value
• The data are separated into a set of vertical thematic layers
• One item of information stored for each location within a single layer
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Types of tessallation
• Regular tessalationsRasters
• Irregular tessalationsQuadtreesVoronoi TessalationsTriangulated Irregular Networks
(TINs)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The raster
• “Raster Data are spatial data expressed as a matrix of cells or pixels, with spatial positioning implicit in the ordering of the pixels” (AGI 1994)
• Raster data structure widely used in GIS e.g. IDRISI, GRASS, Arc/Info’s GRID module
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
The geometry of a raster• Square cell
Adjacency defined by edges and corners
Connectivity to four neighbouring cells
Uniform orientation throughout the matrix
Strong self-similarity Easy decomposition into identically-
shaped unitsVery efficient way of packing space
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Why use rasters?
• Raster data from other disciplines
• Ideal for representing continuous variations in space
• Common way of structuring digital elevation data
• Assumes no prior knowledge of the phenomenon
• Uniform, regular sampling of reality
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Why use rasters?
• Often used as common data exchange format
• Raster algorithms often simpler and faster
• Easy to program, less need for special hardware
• Raster systems tend to be cheaper than vector
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Issues and trade-offs
• May give very large data files typical raster databases may contain >
100 layers each layer typically contains hundreds or
thousands of cells
• Many options exist for storing raster data
some are more economical than others in terms of storage space
some more efficient in terms of access and processing speed
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Issues and trade-offs
• Maximum resolution determined by the size of grid
• Less easy to connect tabular (attribute) data to spatial objects
• Raster data lack topology
• Regular geometry of raster cells may not accurately reflect the variations of reality
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Variable-resolution tessalations
• Triangulated Irregular Networks (TINs)Alternative to regular raster for terrain
modellingDeveloped in 1970s Can build surfaces from irregular arrays of
point elevation dataMany commercial GIS now offer TIN
capabilities.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Topic 4: Coordinates, Datums, and Projections
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Spherical CoordinatesSpherical “grid” is called a graticuleLatitude references north and southLongitude references east/westLine of constant latitude is a parallelLine of constant longitude is a meridianMeridians converge at the poles
Latitude range: 0 to 90 degrees north and southLongitude range: 0 to 180 degrees east and west
0º LatitudeP
rim
e M
erid
ian
0º
Lo
ng
itu
de
Equator
90º N Latitude
90º S Latitude
SouthernHemisphere
NorthernHemisphere
EasternHemisphere
WesternHemisphere
90º W Longitude
0º L
on
git
ud
e
1
80º
Lo
ng
itu
de
90º E Longitude
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Spherical CoordinatesA spherical coordinate measure is expressed in degrees (º), minutes (‘) and seconds (“)
1º = 60’ = 3,600” ; 1’ = 60”
Expressed as:ddd mm ss N/S, ddd mm sss E/W
Note the convention is to express latitude (y) before longitude (x), but computer environments use x,y
• In most digital environments, degrees, minutes and seconds are converted to decimal degrees: degrees + (min/60) + (sec/3600)• Harrisburg International Airport is: 40º12’N, 76 º45’W, or40.20N, 76.75W
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Spherical Coordinates
Eastern and Northern Hemisphere: +x, +y
Eastern and SouthernHemisphere:+x, -y
Western and Northern Hemisphere: -x, +y
Western and SouthernHemisphere:-x, -y
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Cartesian Coordinates
X axis
Y a
xis
0,0 1 2 3 4 5 6 7 8 9
1
2
3
4
5
6
(2.0,3.0)
(4.5, 4.5)
(7.0,2.0)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Horizontal Datum
North American Datum of 1983• an earth centered datum where the center of
the spheroid is the center of the earth • based on the Geodetic Reference System of
1980 (GRS80): a better approximation of earth’s true size and shape.
• twice as accurate as the NAD27: resulted in controls shifted up to 100 meters
North American Datum of 1927• A local datum centered on the Meades Ranch
in Kansas. Surface of ellipsoid was tangent to the Meades Ranch
• 300,000 permanent control network
• Clarke 1866 spheroid used to define the shape and size of the earth
Meades RanchKansas
EarthCenter
Clarke 1866Center
Clarke 1866 Spheroid
GRS80 Spheroid
Meades RanchKansas
EarthCenter
Clarke 1866Center
Clarke 1866 Spheroid
GRS80 Spheroid
NAD 1927 DATUM
NAD 1983 DATUM
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Vertical Datum
North American Vertical Datum of 1988
• 1929 datum adjusted based on more precise measurements of geoid shape and mean sea levels.
• some bench mark heights changed up to 2 meters, but heights between adjacent benchmarks changed < a few millimeters
• provides better geoid height definitions in order to convert earth centered GPS derived heights
National Geodetic Vertical Datum of 1929
• vertical datum based mean sea level as determined by years of observations at tidal gauging stations
• 585,000 permanently monumented vertical benchmarks interconnected by leveling
Vertical Datum(mean sea level)
Land Mass
Sea Floor
Sea Level
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Projections
To represent a spherical model of the earth on a flat plane requires a map projection!
Projection
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map ProjectionsZ = rotational axis
Y
X
o a
b
a
Spheroid: a three-dimensional geometric surface generated by rotating an ellipse about one of its axes.
It provides an approximate model of the earth’s shape, the first step in constructing a projection
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale• Options to deal with minimum mapping unit
size at desired design scaleAdopt a larger map scale for the source
Increased cost for acquisition Increased storage for larger data volume
Convert area features to points or lines Evidence of feature is retained Inconsistency in feature representation May give up desired metrics (area, perimeter) May give up overlay analysis options
Eliminate small areas Consistency in feature representation No evidence of omitted features
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
PennsylvaniaStatewide Projection
• Projection: Lambert Conformal Conic• Spheroid: GRS80• Central Meridian: 77º 45’ 00.0” W (-77.75)• Standard parallels: 40º 36’ 10.8” N (40.603) 41º 16’ 33.6” N (41.276)• Reference latitude: 39º 19’ 59.9’ N (39.333)
Considerations for selecting a statewide projection for Pennsylvania:• Pennsylvania’s east/west extent is best suited for a conic projection • If you need to preserve area, use Alber’s Equal Area Conic • If you need to shape and angle, use Lambert Conformal Conic • Select two standard parallels that divide the state into approximately even
thirds north to south • Select a central meridian that divides the state approximately into equal halves
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projections
• Transform spherical geographic space to a 2-D planar surface.If it is a map, it has been projected!Eliminates need to carry a globe around in
the pocket!2-D Cartesian coordinate space is better suited
than spherical coordinates when conducting traditional surveys, mapping, and ground measurements.
• Ensures a known relationship between map location and earth location
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projections
CYLINDRICAL PLANARCONIC
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projections• A tangent projection results in 1 standard
parallel
• A secant projection results in 2 standard parallels
• A standard parallel is the mathematical point of intersection between the projection plane and the sphere.
• Scale distortion. The scale is true (1) along the standard
parallel(s). The scale is greater than 1 outside of the
standard parallel(s) On secant projections, the scale is less than 1
between the two standard parallels
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projections
• Any representation of the Earth’s 3-D surface on a 2-D plane involves distortion of one or more of the following:shapeareadistance (scale)direction (angle)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projections
• There are many map projections • Each one is good at representing one or
more spatial properties• No projection can preserve all four
properties• The goal is to select a projection that best
matches the intended use of the map. • Projection distortion significantly affects
the properties of a small-scale map• Large scale maps are less effected by
projection distortion
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projection Distortion• Conformal projections
Preserve relative angle and shape for small areas, but area is very distorted
For any given point, local scale is constant in all directions
Used for navigation, meteorological charts Examples: Mercator and Lambert Conformal Conic
• Equivalent projections Preserve area but shape and angles are very distorted. A coin placed at any location on the map covers the
same amount of area Use when area conveys meaning (thematic maps
showing density) Examples: Albers Conic Equal Area and Peters
Projection
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Projection Distortion
MERCATOR (Conformal)
ROBINSON
PETERS (Equivalent)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Universal Transverse Mercator (UTM)
DA
EMB
C • The cylinder is made secant to the sphere, cutting into the sphere along the lines AB and DE
• Lines AB and DE are standard meridians 360,000 meters apart. The scale is exact (1) along these lines.
• The scale for the area between the standard meridians is < 1 (scale too small). Outside these meridians, the scale is too large (> 1)
• Line CM is the Central Meridian, which starts and stops at the poles
• The UTM projection is applied every 6º, resulting in 60 UTM zones for the earth (360 / 6 = 60)
• Good projection if map extent falls within a zone. Should not be used if map extent spans multiple zones
• Used as State Plane projection system for states that are predominately N-S orientation (e.g. Vermont, Maine, Idaho)
0 mN10,000,0000 mS
320,
000
mE
EMB
DCA
680,
000
mE
500,
000
mE
0º 00’ 00”
80º 30’
84º 30’
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Universal Transverse Mercator (UTM)
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Universal Transverse Mercator (UTM)
Cen
tra l
Me r
idia
n
Cen
tra l
Me r
idia
n
Sta
nd
ard
Me r
idia
n
Sta
nd
ard
Me r
idia
n
Sta
nd
ard
Me r
idia
n
vv
UTM ZONE 17 UTM ZONE 18
81º
W
75º
W
72º
W
78º
W
84º
W
• Pennsylvania falls between two UTM Zones: Zone 17 and 18• Using either zone for a statewide projection causes excessive scale distortion• Defining a custom UTM zone with a Central Meridian at 78º W and Standard
Meridians at 81º W and 75 º W would be a better customized use of the UTM projection for PA.
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Pennsylvania State Plane Coordinate System
• Based on two different applications of the Lambert Conformal Conic Projectionresults in two different zones: a North and
South Zone
• Minimizes scale and angle distortions for use by surveyors
• Local governments are required by State Law to use the PA State Plane Coordinate System
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Pennsylvania State Plane North Zone
Scale: 1.000000
Scale: .9999568
Scale: 1.000000
Standard Parallel
Standard Parallel
Central Parallel
Cen
tral
Mer
idia
n77
º 45
’W
Projection Origin40º 10’N, 77º 45’W
40º 53’N
41º 57’N
41º 25’N
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Pennsylvania State Plane South Zone
Scale: 1.000000
Scale: .9999595
Scale: 1.000000
Standard Parallel
Standard Parallel
Central Parallel
Cen
tral
Mer
idia
n
77º
45’W
Projection Origin39º 20’N, 77º 45’W
39º 56’N
40º 58’N
40º 27’N
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Pennsylvania State Plane Origin Offsets For North and South Zones
X offset: 2,000,000’y offset: 0’
projection origin for both Zones: 2,000,000’, 0’
2,000,000’
x min 1,188,150’y min 153,500’
x max 2,813,400’y max 677,900’
2,000,000’
x min 1,204,600’y min 162,000’
x max 2,805,600’y max 771,700’
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• Map scale: the relationship between map distance (or display distance) and actual ground distance
• Scale Calculations:Scale = map distance / (ground distance x conversion
factor)To determine map scale when map and ground
distances are known: 2.5” on map = 500 feet on ground 2.5/500*12 = 2.5/6,000 = 1:2,400
To determine ground distance when map scale is known:
1:4,800 is same as 1” = 4,800” 1.82” on map: 1 * 1.82 = 4,800*1.82 1.82” = 8,7376” = 728’
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• Scale can be expressed as:Linear scale
Graphic scale bar
Correct if map is enlarged or reduced
Verbal scale statement 1 in = 2,000 ft Frequently used by engineers or architects
Representative fraction (RF) 1:24,000 (ratio is correct with any units) Usually used by cartographers
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale• Small Scale Maps
Large denominator in RF (1:14,000,000)Maps of continents and world maps
• Medium Scale MapsMedium denominator in RF (1:24,000)USGS Topographic Quadrangles
• Large Scale MapsSmall denominator in RF (1:2,400)Tax maps, utility maps
• The smaller the number in the denominator, the larger the map scale½ is “larger” than ¼ and ¼ is “smaller” than ½
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• Considerations for selection of source scalecostrequired accuracydesired output map scale(s)desired feature representationdensity of features to be displayed
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• In a GIS, scale is a function of:source map scale (compiled scale)desired plot scale(s)
• Digital data can be plotted at any scaleaccuracy is only as good as the original
source scaleresolution of the data will become apparent
if plot scale greatly exceeds source scale
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
• Map scale sets boundary for feature resolution
• Feature resolution is defined as :The density of features that can be shown at a given
scale
The amount of detail (density of vertices) that can be used to represent a feature at a given scale
Map Scale
woodsoror
or
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• Feature resolution is defined as :Minimum mapping unit: the smallest area feature
that can be effectively discerned at plot scaleGenerally around .15” as measured on map
1:24,000 (300 ft. on ground = .15” on map) 1:4,800 (60 ft. on ground = .15” on map) 1:2,400 (30 ft. on ground = .15” on map) 1:1,200 (15 ft. on ground = .15” on map)
60’
30’15’ f(scale) =
Some of this material was presented by Bruce Stauffer, Advanced Technology Solutions, Inc., and Todd Bacastow, Penn State, at a PA GIS Conference
Seminar, June 2001
Map Scale
• Area features smaller than the minimum mapping unit are:Merged into surrounding data Converted from area to line (drainage)Converted from area to point (cities)Deleted/omitted
LARGER SCALE1:60,000
SMALLER SCALE1:8,000,000
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