Once you understand the structure of the entries in the MAPINFOW.PRJ file, you are ready to create a new projection entry for your coordinate system. You may want to make a copy of the MAPINFOW.PRJ file in case you want to revert back to it later.
To create a new projection entry for the coordinate system in the MAPINFOW.PRJ file:
- Open MAPINFOW.PRJ in a text editor or word processor. In this file, you are going to add the new projection entries.
MAPINFOW.PRJ in Notepad
- Scroll down in this list to find the type of projection you want to base your map on. See Understanding Coordinate Systems for descriptions of the different projection types.
- Add a new line at the end of the projection list you are modifying.
For example, to add a new Universal Transverse Mercator projection (Australian Map Grid using AGD66 datum), scroll down to that entry and type the new projection at the end of the list.
Adding a Line in the MAPINFOW.PRJ File
- On a new line, type the new parameter entries based on the required parameters described for that projection type in the table Projections and Their Parameters.
- If the name of your projection does not appear in the Common Map Projections list, consider the kind of projection you are creating (Latitude/Longitude, Conic, Transverse, etc.) and follow the table entries for the type of projection you want.
- Remember to include constant values (Accounting for Affine Transformations and Explicit Bounds in Projection Types) to indicate an affine transformation, specific bounds, or both if appropriate or necessary.
Note: The order of parameters is vitally important. Remember to separate each parameter with a comma.
- Save your edited MAPINFOW.PRJ file in the directory in your user directory.
Note: In the past the MAPINFOW.PRJ file was saved in your installation directory but this did not allow different users to have different PRJ files. This new file placement permits this.
Things to keep in mind when editing the MAPINFOW.PRJ file:
- You must record the X and Y coordinates of the origin point in decimal degrees.
- Remember to include a negative sign for west longitudes and south latitudes.
- You must list the origin longitude first in the MAPINFOW.PRJ file entry.
- Carry out decimals to at least five (5) places for greater accuracy.
- Do not use commas to represent thousands or millions in large numbers. Only use commas to separate parameters from one another.
- When specifying projection, datum and units, use the number that represents the parameter. These numbers are listed in the table for each parameter earlier in this section. In our example, 6 represents Equidistant Conic projection; 74 represents NAD 83 datum, and 7 represents meters.