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Geographic Information Systems

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

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Geographic Information Systems

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  1. Geographic Information Systems GIS Analysis and Modeling

  2. 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 - what will happen at where in the future or in other locations

  3. 2. Organizing Geographic Data • Data layers (shape file etc.) • Feature types: points, lines, polygons • Object types: geometric or thematic e.g. Development streets - line layer1 water - line layer2 parcels - polygon layer1 soils - polygon layer2

  4. 3. Maintenance of the Spatial Data • Format transformation - Spatial data files must be transformed into the data structures and file formats used internally by a GIS software package • Geometric transformation - Different data layers should be registered to a common coordinate system

  5. 4. Maintenance of Attribute Data • Attribute editing - List, add, delete, redefine, etc. • Attribute query - Retrieve attributes according to certain criteria

  6. 5. Integrated Analysis of Spatial and Attribute Data • The power of GIS lies in its ability to analyze spatial and attribute data together • Retrieval, classification, and measurements • Overlay

  7. 5. (1) (i) Retrieval • Selective search without modifying the original data (for output) http://www.sdsmt.edu/online-courses/geology/mprice/geo416/lecture9.ppt

  8. 5. (1) (ii) Classification • Attribute data - cerate a new attribute item based on existing ones • Spatial data -spatial features may be aggregated to larger entities e.g. Recode in a raster environment Dissolve in a vector environment • Single layer vs. multiple layers (overlay)

  9. Classification Raw data Classified data http://www.geog.leeds.ac.uk/courses/level2/geog2750/geog2750_15.ppt

  10. 5. (1) (iii) Measurement • Distances between points • Nearest distances • Functional distances • Lengths of lines • Perimeters and areas of polygons • Centroid of an area • Area of a profile • Volume • Shape • Narrowest and broadest distances across a polygon • Sinuosity of a line

  11. 5. (1) (iii) Measurement • Distances between Points - Euclidian distance

  12. 5. (1) (iii) Measurement • Nearest distances The Closest Facility

  13. 5. (1) (iii) Measurement • Functional Distance Three-minute response time from a fire station, City of Phoenix http://www.esri.com/mapmuseum/mapbook_gallery/volume17/public2.html

  14. 5. (1) (iii) Measurement • Lengths of lines • Perimeters and areas of polygons

  15. 5. (1) (iii) Measurement • Centroid of an area • It is used to represent a polygon by a single point • Several methods to identify a centroid: mean value of vertices’ coordinates, center of the enclosing circle or rectangle, http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

  16. 5. (1) (iii) Measurement • Area of a profile • Volume

  17. 5. (1) (iii) Measurement • Shape - how to measure shape of an area? - a compact shape has a small perimeter for a given area • compare perimeter to the perimeter of a circle of the same area - shape = perimeter / area • Narrowest and broadest distances across a polygon

  18. 5. (1) (iii) Measurement • Sinuosity of a line - the ratio of the actual length to the straight line length between point A and point B

  19. 5. (2) Overlay • Arithmetic overlay • Logic overlay • Weighting input layers • Raster vs. vector overlay

  20. 5. (2)(i) Arithmetic Overlay • adding layers, subtracting, multiplication, division, etc. • Raster Input data layer A Input data layer B Output data layer

  21. 5. (2)(i) Arithmetic Overlay • Arithmetic operation on two data layers using the vector data model Attribute data Spatial data Input data layer A Input data layer B Output data layer

  22. 5. (2)(ii) Logic Overlay • Finding areas where certain conditions occur • Boolean logic Mary Ruvane, UNC –Chapel Hill

  23. 5. (2)(iii) Weighting Input Layers • Professional experiences • Expert votes • Empirical or analytical models

  24. 5. (2)(iv) Raster vs. Vector Overlay • Raster - Every cell is executed, and the overlay result is a new layer • Vector - The operation is executed only for areas of interest • - New attribute items are created • - New layers may be created that carry both the original and new attributes - The operation is generally more complex than raster overlay

  25. Raster Overlay Vector Overlay http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

  26. Readings • Chapter 5,6,9,10

  27. 3.(3) Conflation • The procedure of reconciling the positions of corresponding features in different data layers (e.g. snapping).

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