UNIT 14 - VECTOR GIS CAPABILITIES

UNIT 14 - VECTOR GIS CAPABILITIES

Compiled with assistance from Holly J. Dickinson, State University of New York at Buffalo


For Information that Supplements the Contents of this Unit:

Buffers: Distance Transformations (Chrisman/U of Washington) -- Graphics and information about: construction of buffers; generalized Voronoi diagram; Voronoi zones around points.
Transformations Examples (Chrisman/U of Washington) -- Dasymetric mapping of population density; wastelands vs. wetlands; review of operations and transformations; after point in polygon; after point in polygon overlay; etc.
Transformations Between Measurement Frameworks (Chrisman/U of Washington) -- Surface transformations; taxonomy of transformations.


This unit would be illustrated well with a series of overlays of a real area which demonstrates the problems discussed here using simple examples.

UNIT 14 - VECTOR GIS CAPABILITIES

A. INTRODUCTION

B. SIMPLE DISPLAY AND QUERY

Display

Standard Query Language (SQL)

Boolean operators

SQL extensions for spatial queries

C. RECLASSIFY, DISSOLVE AND MERGE

Steps

Forestry example

City zoning example

D. TOPOLOGICAL OVERLAY

Point in polygon

Line on polygon

Polygon on polygon ("Polygon overlay")

Example

Spurious polygons

  • the small, invalid polygons are called spurious or sliver polygons and can be a major problem in polygon overlay

  • spurious polygons arise when two lines are overlaid which are actually slightly different versions of the same line
  • the problem cannot be removed by more careful digitizing - more points simply leads to more slivers

  • some GISs allow the user to set a tolerance value for deleting spurious polygons during overlay operations

    E. BUFFERING

    REFERENCES

    Documentation for ARC/INFO (user manuals, Understanding GIS) provides an overview of vector GIS functionality for a commonly available system.

    Burrough, P.A., 1986. Principles of Geographical Information Systems for Land Resources Assessment, Clarendon, Oxford. Chapter 5 on data analysis.

    Lusardi, Frank, 1988. The Database Expert's Guide to SQL, McGraw-Hill Book Co., New York. Good introduction to Standard Query Language.

    EXAM AND DISCUSSION QUESTIONS

    1. Compare the buffer function in raster and vector systems, in terms of results, options offered by systems, and flexibility.

    2. The skeleton function moves the boundary of an area object inwards rather than outwards. Show how this would work using a simple diagram, and what happens as the amount of movement increases. What objects might be created by this operation, and what uses can you devise for them?

    3. What are spurious polygons and what characteristics of data cause them?

    4. Section D listed three types of topological overlay between points, lines and areas. Are there others? What applications might they have?


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