Geographical Information Systems

Geog 481/506                                                                                                  Tu Th 3:30-4:50pm
Fall 2011                                                                                                          Fillmore 170

Instructor: Ling Bian                                                                                          LabA: Tue:   5-6:20pm, W145, Chunyuan Diao
Office: 120 Wilkeson                                                                                        LabB: Thur:  6:30-7:50pm, W145, Tong Sun
Office hours: Tu Th 2-3pm  or by appt.                                                             LabC: Fri:  10-11:20am, W145, Tong Sun

GIS Analysis Functions 

1. Geographic analysis

    Geographic questions: where, when, why, and how
    The purpose of the analysis is to answer questions about what existed in the past,
    what exists now, and what will happen in the future or in other locations.
 
2. Organizing geographic data
    Data layers (coverage etc.)
    Feature types: point, lines, polygons
    Objects: geometric or thematic
 
3. Maintenance of the spatial data
            (1) Format transformation
            Spatial data files must be transformed into the data structures
            and file formats used internally by a GIS software package
(2) Geometric transformation
            Different data layers are registered to a common coordinate system
(3) Conflation
            A procedure of reconciling positions of corresponding features
            in different data layers (e.g. snapping).
 
4. Maintenance of attribute data
            Attribute editing: list, add, delete, redefine, etc.
            Attribute query: retrieve attributes according to certain criteria
 
5. Integrated analysis of spatial and attribute data
    The power of GIS lies in its ability to analyze spatial and attribute data together
 
    (1) Retrieval, classification, and measurements
            Retrieval: selective search without modifying the original data (for output)
 
            Classification
                        Attribute data: cerate a new attribute item based on existing ones
                        Spatial data: spatial features may be aggregated to larger entities
                                Recode in a raster environment
                                Dissolve in a vector environment
                        Single layer vs. multiple layers (overlay)
 
            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
 
    (2) Overlay
            Arithmetic overlay: adding layers, subtracting, multiplication, division, etc.
 
            Logic overlay
                        Finding areas where certain conditions occur
                        Boolean logic
 
            Weighting input layers
                        By: Professional experiences
                              Expert votes
                              Empirical or analytical models
 
            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
                        union

                        identity

                        intersect

                        erase

                        update