Lecture 4: Spatial Analysis (Vector)

I. Spatial Analysis Workflow

• Spatial Analysis

  • Spatial analysis is a set of techniques for analyzing spatial data

  • The results of spatial analysis are dependent on the locations of the objects being analyzed

  • Software that implements spatial analysis techniques requires access to both the locations of objects and their attributes

  • In GIS, it normally follows this sequence of operations:

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II. Analytical functions for vector data

GIS Analysis Functions

• Intravariable - performed on a single data set

• Intervariable - performed on two or more data sets

• Querying

  • Method of data retrieval

  • Can be performed either on data that are part of the GIS database or on new data produced as a result of data analysis

    

• Distance / Proximity Analysis

  • Buffer

    • Creation of a zone of interest or new layer boundary (buffers) at specified distance from input layer

      • Point entity: circular buffer zone

      • Line entity: elongated buffer zone

      • Polygon entity: buffer zone has the same shape as original polygon, but larger

  • Point distance tool

    • Calculation of distance from each point in one feature class to all points given a search radius to another feature class

      

    • Ex: Crime incidence vs Police Stations

  • Near tool

    • Adds attribute fields to a point feature class containing distance, feature identifier, angle and coordinates of nearest point / line

      

    • Example: Find the closest established benchmark from the river network

  • Thiessen polygons

    • Creates a polygon of the areas closest to each feature for a set of input feature

      • target’s zone of influence or “catchment area”

      • partitioning of the plane into polygons that have this characteristic, that is containing all the locations that are closer to the polygon’s ‘midpoint’ than to any other midpoint

        

• Vector Overlay Analysis

  • New spatial data layer from two or more old data layers

  • Can be done within vector and raster

  • Should be georeferenced in the same coordinate system; and

  • Should cover the same area of interest

  • Basic principle:

    • Compare the properties of the same location in both data layers, and to produce a new characteristic for that location in the output layer.

  • Individual data layers to be overlaid have to be topologically correct

    • lines should meet at nodes and polygon boundaries are closed

    

  • A spatial join involves matching rows from the join layer to the target layer based on a spatial relationship and writing to an output feature class

  • When a match is found during processing, a row is added to the output feature class containing the shape and attributes from the target layer and the matching attributes from the join layer

    

III. Examples and Applications

• check powerpoint ;>