| iTool User's Guide: Working with Vectors |

## Vectors and Mapping

If you insert a map projection into an iTool with an existing vector visualization, or if you insert a vector visualization into an iTool with an existing map projection, IDL will attempt to determine whether the vector visualization should be warped using the current map projection.

If the X coordinates of the vector visualization are in the range from -180 to 180 and the Y coordinates are in the range from -90 to 90, the locations of the vectors are assumed to represent longitude and latitude. In this case, the location of each vector is warped to the current map projection. If the X and Y coordinates are not in this range, the vector locations are not warped.

Note The locations and directions of vectors are warped, but their magnitudes are not. The magnitude is assumed to be independent of the grid units.

You can override the default behavior by setting the Grid units property of the vector visualization or by specifying the value of the GRID_UNITS keyword to IVECTOR:

- Setting the value of the Grid units property to `1` (meters) indicates that the vector locations are already correctly located on a particular map projection (assumed to be in meters). In this case, you should then also set the dataspace map projection to match your map projection, so that any images or shapefiles are warped to the correct map projection.

- Setting the value of the Grid units property to `2` (degrees) indicates that the vector locations are in degrees of longitude and latitude, and that these locations should be warped to the map projection.

- Setting the value of the Grid units property to `0` (Not applicable) indicates that the vector grid is in arbitrary units that are not tied to a map projection.

IDL Online Help (March 01, 2006)