Map Projection

The map projection options are available in several MapViewer commands such as Calibrate, Import (when projection is Unknown), Base Map, and Reproject Data File. The Coordinate System page of the plot properties also contains projection information and options.

Projection

Choose a projection in the Assign Coordinate System dialog. If the projection has options, click the Settings button to open the Modify Projection Settings dialog. The options in this dialog vary depending on which projection is selected. Refer to the specific projection in online help for more information on the specific options. If State Plane 1927, State Plane 1983, or Universal Transverse Mercator is selected, choose the appropriate zone in the Zone list.

Map Limits

The Map limits section displays the limits of the current map in the map window. This information can be helpful when redefining a projection and its associated parameters.

Datum

See the Datum topic for detailed information on datum. In the Map Projection dialog, check the Apply datum conversion check box to activate the Datum list and then select the datum you wish to use. If you select the User Defined datum, click the Custom button to define the datum.

Apply Datum Conversion

When the Apply datum conversion check box is checked, the datum conversion is applied during the projection change. If this check box is not checked, the datum conversion is ignored.

To use a different datum:

1. Click the Map | Plot | Plot Properties command and click the Change... button in the Coordinate System page of the Property Manager.

2. Select a coordinate system in the Assign Coordinate System dialog. Click the Modify... button to change the datum.

3. Select the datum you wish to use in the Datum list of the Define Coordinate System dialog. If the datum selected is User Defined Datum, you also need to specify the parameters for the datum by clicking the Custom button and entering the appropriate parameter values in the Custom Datum Definition dialog that appears. Click the OK button to store the parameters and return to the Map Projection dialog.

4. Click the OK button.

MapViewer modifies the coordinates of the drawing for the new datum. This may take a few minutes if the drawing is large.

Importing Files

When you use Map | Base Map or File | Import to import a file that does not contain projection information in it, you are prompted to select the projection information. If you know the projection, datum, and data units, use this dialog to set the file information. If you do not know all three pieces of information, leave the Projection set to Unknown. Do not use this dialog to change the projection, datum, or file units as this causes the map to import incorrectly. Use Map | Calibration to change the map settings.

Input Data Units

When you initially import a file that does not contain projection information, an Input data units list appears in the Import Options dialog. Select the units contained in the file.