Creating maps

A good way to create maps that show geographic features and a few plate tectonic features is via the web site at http://www.aquarius.geomar.de/omc/

You will need the following information, which is best assembled before you start.

1. The parallels of latitude and meridians of longitude that form the sides of your map.

BEFORE making a map, be sure you understand the principles of latitude and longitude. These coordinates are required to outline your map area.

Entering the values of latitude and longitude incorrectly is the most common source of error.

All northern hemisphere parallels are given as positive numbers, latitudes in the southern hemisphere are given as negative numbers. Meridians east of Greenwich (up to 180) are positive numbers; meridians west of Greenwich (to 180) are negative numbers. You can also treat meridians west of Greenwich as positive numbers by remembering that the numbers increase to the east. Thus Philadelphia is either at -75 (west longitude) or 285 (360-75). The westernmost meridian must be on the left and the northernmost parallel must be on the north.

2. The map projection. Various projections available are explained on the web page by clicking on map projection in the material covered on the web page in the paragraph entitled: What do I need to know to draw a map? For small areas I recommend the Mercator projection except at the poles where you should use Polar Stereographic. For large areas like continents and hemispheres, use Lambert Azimuthal Equal-Area Projection.
3. Decide which of the following you will want to show: political boundaries, rivers, cities, topography, etc. The options are given on the map creation form.
4. You can also chose some plate tectonic features to show. Not all features are available. Try various options and see what you get.
5. You can select either a colored map (land yellow, water blue) or a black and white map.
6. TO PRINT A MAP - If you want to save and print your map you must select either Postscript or Adobe Illustrator under the Download option in the middle of the form under the Map Projection selection. If you do not select either of these options the download button on the toolbar of the map output page will be disabled.

• To save, click on the download button on the toolbar of the map output page. In the small box that opens click on Save File. A window then opens that permits you to indicate a directory for saving the file. You should save to a floppy or zip disk. If you are saving to a floppy disk then select the A: directory. The default file name will be something like 18134.ps.gz The .ps tells this is a postscript file and the .gz tells that the file is compressed using gzip. You can save this file with a different name BUT you must keep both the ps and the gz extensions. So a new name might be: mymap.ps.gz
• To decompress run the WINZIP program.
• The EPSF (postscript) and Illustrator files can be imported into a variety of graphic packages. In the Geology Dept. we use CANVAS as a graphics program. Canvas will read these files. They can then easily be edited by the user, for instance by changing the colors.

The details of the procedure are explained in the web site as you go. If you have questions be sure to check with an instructor.

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