Thiessen Polygon Application v5.0

General Overview Thiessen polygons, also referred to as the Dirichlet Tessellation or the Voronoi Diagram, define the indivdual 'regions of influence' around each of a set of points. Thiessen Polygons divide a plane, assigning the area to point in the set such that any location within a particular polygon is nearer to that polygon's point than to any other point. Mathematically, a Thiessen is defined by the perpendicular bisectors of the lines between all points. One of the most widespread uses of Thiessen Polygons is the delineation of the marketshed of retail or service nodes (eg. malls, stores, hospitals); Walter Christaller's Central Place Theory is the classic application of this locational tool within that field. Thiessen Polygons are used to predict the values at surrounding points from a single point observation, as in the fields of hydrology/hydrogeology (water sampling) and climatology (rain gauges). Thiessen Polygons have also been utilized to generate the center-line street network for a series of roads that had been digitized as polygons. This application provides three programs for the computation of Thiessen Polygons: Windows Program: SDF File Preparation for MapGuide Author Permits off-line generation of an SDF file containing Thiessen Polygons generated for a set of points read from an ASCII file. The SDF file may then be added as a layer to an MWF via the MapGuide Author. CGI Program: Server-Side Computation The CGI program provides for Server-Side computation of Thiessen Polygons for points submitted as an input parameter, or obtained by the program as a user-defined relational database query. The SDF file is output to a directory, where it may be accessed as an MWF layer in order to send the results back to the client. ActiveX Control: Client-Side Computation The ActiveX Control supports Internet Explorer applications to generate Thiessen Polygons on the client-side. The control accepts a set of MapGuide Viewer API objects, computes the solution, and permits access to the results through set of public function calls via JavaScript or VBScript. The results may then be portrayed through the MapGuide Viewer as a Redline Layer. The application also includes an SDF Viewer that enables the graphic display of one or more SDF files. The SDF Viewer permits immediate viewing of SDF files without the need for authoring maps or conversion to another format. Contact Hunter GIS to order MapGuide Thiessen Polygon Solutions customized to your data and business requirements.

© 2006, Hunter GIS