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| The GMAP Procedure |
Overview
The GMAP procedure produces two-dimensional (choropleth) or three-dimensional (block, prism, and surface) maps that show variations of a variable value with respect to an area. A wide assortment of map data sets is available with SAS/GRAPH software.
Use the GMAP procedure to perform the following tasks:
| About Block Maps |
Block maps display a block at the approximate center of each map area to convey information about response variable values. The height of each block is directly proportional to the value of the response variable.
Note: If the map area consist
of multiple, noncontiguous areas, then the block is centered over the largest
polygon of the set. For example, in the case of Japan the block is centered
over the largest island which is Honshu. ![[cautionend]](../../../../common/63294/HTML/default/images/cautend.gif)
Block Map shows a simple block map of the populations of countries in Asia. The population of each country (the response value) is represented by the height of the block.
![[Block Map]](images/gmpsimpl.gif)
The program for this map is in Producing a Simple Block Map. For more information on producing block maps, see BLOCK Statement.
You can assign patterns to the areas in a block map by using the AREA statement. The values of the AREA variable are represented by the pattern of each map area, and the values of the response variable on the BLOCK statement are represented by the height of the blocks. For more information, see AREA Statement.
| About Choropleth Maps |
Two-dimensional (choropleth) maps indicate levels of magnitude or response levels of the corresponding response variable by filling map areas with different colors and patterns.
Two-dimensional (Choropleth) Map shows a choropleth map of the population of countries in Europe. The population of each country (the response value) is represented by the pattern that is assigned to the country.
Two-dimensional (Choropleth) Map
![[Two-dimensional (Choropleth) Map]](images/gmpchoro.gif)
The program for this map is in Producing a Simple Choropleth Map.
You can also produce a simple choropleth map that shows an outline of a map's areas by specifying your map data set as both the map data set and the response data set in a GMAP statement and adding a PATTERN statement with VALUE=EMPTY. For more information on the PATTERN statement, see PATTERN Statement. For more information on producing choropleth maps, see CHORO Statement.
| About Prism Maps |
Prism maps use polyhedrons (raised polygons) in the shape of each map area to convey information about response variable values. The height of each polyhedron, or prism, is directly proportional to the value of the response variable.
You can alter the perspective of the map by selecting a viewing position (the point in space from which you view the map). You can also change the position of the light source so that the shadowing on the prisms enhances the illusion of height.
Prism Map shows a prism map of the populations of countries in Africa. The population of each country (the response value) is represented by the height of the country and the color of the country's map area.
![[Prism Map]](images/gmpprism.gif)
The program for this map is in Producing a Simple Prism Map. For more information on producing prism maps, see PRISM Statement.
You can also assign patterns to the areas in a prism map by using the AREA statement. The values of the AREA variable are represented by the pattern of each map area, and the values of the response variable on the PRISM statement are represented by the height of the map areas. For more information, see AREA Statement.
| About Surface Maps |
Surface maps display a spike at the approximate center of each map area to convey information about response variable values. The height of the spike corresponds to the relative value of the response variable, not to the actual value of the response variable. Thus, a spike that represents a value of 100 might not be exactly 10 times higher than a spike that represents a value of 10. Map area boundaries are not drawn.
Surface maps provide no clear map area boundaries and no legend. Thus, surface maps provide a simple way to judge relative trends in the response data but are an inappropriate way to represent specific response values.
Surface Map shows a surface map of the population growth rates of countries in Europe. The growth rate for each country (the response value) is represented by the height of the spike for that country.
![[Surface Map]](images/gmprosur.gif)
The program for this map is in Rotating and Tilting a Surface Map. For more information on producing surface maps, see SURFACE Statement.
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