Pitney Bowes MapInfo Professional - Manual (Page 286)

• Setting the Default Behavior of the Replace Layer Style Check Box
• Example of Bivariate Thematic Mapping
• Using an Inflection Point to Show Distinction
• Example of an Inflection Point Map
• Controlling the Number of Inflection Values
• Applying Rounding Factors to Inflection Values
• Spreading Inflections by Equal Cell Count
Working with Grid Surface Maps
The thematic maps we have discussed are based on vector layers. MapInfo Professional takes thematic
mapping to a new level with a method that displays data as continuous color gradations across the map.
This type of thematic mapping, known as grid mapping or surface theme mapping, is produced by an
interpolating point data from the source table. MapInfo Professional generates a grid file from the data
interpolation and displays it as a raster image in a Map window.
Grid theme maps are appropriate analytical tools in traditional GIS environments and other industries
where the data points have measured values that reflect those locations. For example, use grid shading
to illustrate temperature changes, snowfall amounts, or change in elevation.
The next figure shows the light to dark gradual transition across the United States, which represents low
to high average annual temperatures. The continuous shading allows you to derive measurements at
places other than where measurements were taken.
Figure: Grid Surface Thematic Map
Grid Image Files
Grid mapping produces a file type called a grid image. When you create a grid thematic map using
MapInfo Professional's grid handler, MapInfo Professional generates a default file name of
tablename_fieldname with the extension .MIG (for example, USELEV_ELEVFEET.MIG). In the Create
Thematic Map - Step 2 of 3 dialog box MapInfo Professional displays the path and the root file name,
where you can change it as necessary.
MapInfo Professional contains one read/write grid handler and a Grid Engine tool kit that shows you how
to create your own. Once you have written a grid engine, you place this file in your MapInfo Professional
application directory and set the preference in the Map Window dialog box. Specifically, to set the default
grid writeable handler, go to the Map window preferences and specify your grid handler file. The available
MapInfo Professional 12.5 286
Working with Grid Surface Maps