geographic information systems

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

Readings Readings

► Chapter 5,6,9,10Chapter 5,6,9,10

3.(3) Conflation3.(3) Conflation

► The procedure of reconciling the positions of The procedure of reconciling the positions of corresponding features in different data layers (e.g. corresponding features in different data layers (e.g. snapping).snapping).