geographic information systems
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Geographic Information Systems. GIS Analysis and Modeling. 1. Geographic Analysis. Geographic questions: where, when, why, and how The purpose of the analysis is to answer questions about: - what existed at where, when, why, and how - PowerPoint PPT PresentationTRANSCRIPT
Geographic Information SystemsGeographic Information Systems
GIS Analysis and Modeling GIS Analysis and Modeling
1. Geographic Analysis1. Geographic Analysis ► Geographic questions: where, when, why, and howGeographic questions: where, when, why, and how
► The purpose of the analysis is to answer questions The purpose of the analysis is to answer questions about:about:
- what existed at where, when, why, and how- what existed at where, when, why, and how
- what will happen at where in the future or in - what will happen at where in the future or in other locationsother locations
2. Organizing Geographic Data2. Organizing Geographic Data ► Data layers (shape file etc.)Data layers (shape file etc.)► Feature types: points, lines, polygonsFeature types: points, lines, polygons► Object types: geometric or thematicObject types: geometric or thematic
e.g. Developmente.g. Development
streets - line layer1streets - line layer1
water - line layer2water - line layer2
parcels - polygon layer1parcels - polygon layer1
soils - polygon layer2soils - polygon layer2
3. Maintenance of the Spatial Data3. Maintenance of the Spatial Data
► Format transformationFormat transformation
- Spatial data files must be transformed into the - Spatial data files must be transformed into the data structures and file formats used internally by a data structures and file formats used internally by a
GIS software packageGIS software package
► Geometric transformation Geometric transformation
- Different data layers should be registered to a - Different data layers should be registered to a
common coordinate systemcommon coordinate system
4. Maintenance of Attribute Data4. Maintenance of Attribute Data
► Attribute editingAttribute editing
- List, add, delete, redefine, etc. - List, add, delete, redefine, etc.
► Attribute queryAttribute query - Retrieve attributes according to certain criteria- Retrieve attributes according to certain criteria
5. Integrated Analysis of Spatial and 5. Integrated Analysis of Spatial and
Attribute DataAttribute Data
► The power of GIS lies in its ability to analyze spatial The power of GIS lies in its ability to analyze spatial
and attribute data togetherand attribute data together
► Retrieval, classification, and measurements Retrieval, classification, and measurements ► Overlay Overlay
5. (1) (i) Retrieval5. (1) (i) Retrieval► Selective search without modifying the original data Selective search without modifying the original data
(for output)(for output)
http://www.sdsmt.edu/online-courses/geology/mprice/geo416/lecture9.ppt
5. (1) (ii) Classification5. (1) (ii) Classification
► Attribute dataAttribute data
- cerate a new attribute item based on existing - cerate a new attribute item based on existing ones ones
► Spatial dataSpatial data
-spatial features may be aggregated to larger -spatial features may be aggregated to larger entities entities
e.g. Recode in a raster environment e.g. Recode in a raster environment
Dissolve in a vector environmentDissolve in a vector environment
► Single layer vs. multiple layers (overlay) Single layer vs. multiple layers (overlay)
ClassificationClassification
Raw data Classified data
http://www.geog.leeds.ac.uk/courses/level2/geog2750/geog2750_15.ppt
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Distances between pointsDistances between points► Nearest distancesNearest distances► Functional distancesFunctional distances► Lengths of linesLengths of lines► Perimeters and areas of polygonsPerimeters and areas of polygons► Centroid of an areaCentroid of an area► Area of a profile Area of a profile ► VolumeVolume► ShapeShape► Narrowest and broadest distances across a polygonNarrowest and broadest distances across a polygon► Sinuosity of a lineSinuosity of a line
5. (1) (iii) Measurement5. (1) (iii) Measurement
► Distances between Points Distances between Points
- Euclidian distance- Euclidian distance
5. (1) (iii) Measurement5. (1) (iii) Measurement
The Closest Facility
► Nearest distancesNearest distances
5. (1) (iii) Measurement5. (1) (iii) Measurement
► Functional Distance Functional Distance
Three-minute response time from a fire station, City of Phoenix
http://www.esri.com/mapmuseum/mapbook_gallery/volume17/public2.html
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Lengths of linesLengths of lines► Perimeters and areas of polygons Perimeters and areas of polygons
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Centroid of an area Centroid of an area ► It is used to represent a polygon by a single It is used to represent a polygon by a single
pointpoint► Several methods to identify a centroid: mean Several methods to identify a centroid: mean
value of vertices’ coordinates, center of the value of vertices’ coordinates, center of the enclosing circle or rectangle, enclosing circle or rectangle,
http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Area of a profileArea of a profile► Volume Volume
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Shape Shape
- how to measure shape of an area? - how to measure shape of an area?
- a compact shape has a small perimeter for a - a compact shape has a small perimeter for a given area given area
- compare perimeter to the perimeter of a circle of compare perimeter to the perimeter of a circle of the same area - shape = perimeter / areathe same area - shape = perimeter / area
► Narrowest and broadest distances across a polygonNarrowest and broadest distances across a polygon
5. (1) (iii) Measurement 5. (1) (iii) Measurement
► Sinuosity of a line Sinuosity of a line - the ratio of the actual length to the straight line - the ratio of the actual length to the straight line length between point A and point Blength between point A and point B
5. (2) Overlay5. (2) Overlay
► Arithmetic overlay Arithmetic overlay ► Logic overlay Logic overlay ► Weighting input layers Weighting input layers ► Raster vs. vector overlay Raster vs. vector overlay
5. (2)(i) Arithmetic Overlay5. (2)(i) Arithmetic Overlay
► adding layers, subtracting, multiplication, division, adding layers, subtracting, multiplication, division, etc. etc.
► RasterRaster Input data layer A
Input data layer B
Output data layer
5. (2)(i) Arithmetic Overlay5. (2)(i) Arithmetic Overlay ► Arithmetic operation on two data layers using the Arithmetic operation on two data layers using the
vector data modelvector data model
Input data layer A
Input data layer B
Output data layer
Spatial data Attribute data
5. (2)(ii) Logic Overlay5. (2)(ii) Logic Overlay
► Finding areas where certain conditions occurFinding areas where certain conditions occur
► Boolean logicBoolean logic
Mary Ruvane, UNC –Chapel HillMary Ruvane, UNC –Chapel Hill
5. (2)(iii) Weighting Input Layers5. (2)(iii) Weighting Input Layers ► Professional experiences Professional experiences ► Expert votes Expert votes
► Empirical or analytical modelsEmpirical or analytical models
5. (2)(iv) Raster vs. Vector Overlay5. (2)(iv) Raster vs. Vector Overlay
► RasterRaster
- Every cell is executed, and the overlay result is a - Every cell is executed, and the overlay result is a new layer new layer
► VectorVector - - The operation is executed only for areas of interestThe operation is executed only for areas of interest
- New attribute items are created - New attribute items are created
- New layers may be created that carry both the - New layers may be created that carry both the original and new attributesoriginal and new attributes
- The operation is generally more complex than raster - The operation is generally more complex than raster overlayoverlay
Raster OverlayRaster Overlay Vector OverlayVector Overlay
http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf