View source for Mapping:Index maps

An index map is an array of integer values (one for each grid cell) that represent unique IDs for the different spatially distributed properties being defined.  The typical maps (although not restricted to) are derived from:

:*A land use (land cover or vegetation cover) coverage.
:*A soil texture coverage.
:*A combination of land use and soil type coverages where all the combinations of land use and soil texture are determined with an ID created for each unique pair of overlapping polygons. 

The ''Maps'' dialog is used to create and manage different index maps used in ''WMS''.  This dialog is shown in Figure 7.

[[Image:Primer Image012.png|frame|none|'''Figure 7.'''  The Index Map dialog. Index maps can be created through generating unique IDs from a GIS coverage or coverages, such as land use, or the entire map may be assigned a single ID through the <br>Constant->Array button. Also, individual cell IDs may be manually modified]]

Several options exist for creating index maps including:

:*Importing an existing grid file.
:*Mapping a GIS coverage.
:*Setting a constant value for all grid cells.
:*Interpolating from a data set. 

The following sections describe the key elements of the ''Index Maps'' dialog.

The Index Maps window contains a list of maps created for the ''GSSHA'' project.  A new map can be created using the ''Add Map'' button, and the ''Rename Map'' button can be used to give it a more meaningful name.  The ''Copy Map'' and ''Delete Map'' buttons can also be used to add or delete maps from the list.  

The ''Import'' button allows a ''GRASS'' ASCII grid to be imported and used as an index map.  The ''Import'' command is primarily used when the ''GRASS'' GIS is used as a companion to ''WMS'' for ''GSSHA'' model development.  The imported grid must be of the same resolution as the ''GSSHA'' grid already created in ''WMS''.  Unless both of these grids are created in ''GRASS'', this is unlikely to be the case.  The ''Export'' command can be used to save an ASCII grid of the selected index map.  This function is most useful if you wish to view the grid with ''ArcView'' or other GIS software.
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