Maps for Scientists: Using

You’ll usually be wanting to work with maps that are EPS graphics, which are the standard for the publishing industry. If you have a Windows Metafile (.wmf), it’s fine for editing inside Word or PowerPoint (here’s a tutorial) but not much else. Personally I prefer to work with EPS files and export them as GIF images when I need to use them in a PowerPoint show. The workflow below is for Illustrator, but other vector graphics packages should work similarly.

maptextfile.gifYour map may start off in PostScript or Illustrator format. PostScript is a language used to define the lines and curves that make up vector graphics; a PostScript file looks like an ordinary text file, and indeed you can open it with a word processor, although it’s scarcely enthralling reading. Once you open it in Illustrator or any other vector graphics program that speaks openmaptextfile.gifPostScript, it will display as a series of shapes with lines and fills. It’s also possible to buy maps already saved in Illustrator format, which allows them to have complex layering and makes them easier for you to edit. Older Illustrator maps will need to have their fonts updated when you open them in Illustrator CS; this is an option you’re given when you first open them, and there’s no going back. Use Save As to make a working copy of the original. Of course, you should be using Save As all the time anyway to make multiple working versions of any graphic you’re editing. Go on, you’ll thank me one day.


If the graphic has layers, turn off or delete the ones you don’t want. If it doesn’t have layers, similar objects (land, sea) are probably arranged in groups, so you can select them all with a single click. Sometimes, though, there are just too many points on a complex path (for example, a detailed coastline) for it to be a single Illustrator object. If that’s the case, and the things you want to change are tiled or split into several groups, you have two choices. You can shift-click to select multiple objects, or you can do a Select > Same (for example, Same > Fill Color) to catch everything sharing the properties of what’s already selected. This is useful for catching every last one of a cloud of things like rivers or placenames if they’re not handily grouped.


When you have a group of objects selected, I’d recommend converting them to grayscale, since most maps you make will have to be reproduced in black and white at some point. You can pick a color model from the popup menu in the Color palette. (You know those little triangles popup.gif are popup menus, don’t you? Not everyone does.) Make sure the shades of gray are far enough apart to remain distinctive after printing or photocopying (perhaps at least 20%), and avoid less than 15% or greater than 85%, as these will degrade to solid white or black after a couple of rounds of photocopying. In this map, the pale blue ocean converted to 9% Black when I switched to grayscale, so I bumped it up to 15%.


If you don’t need all the layers in an object, you can delete them, but sometimes you’ll just want to hide them in case they’re needed one day. These invisible layers are still included when you send something to the printer or export it as an EPS, which can have a big effect on file size. To keep an invisible layer available but not have it included when you print or export, uncheck the Print checkbox in the Layer Options dialog, which is in the Layers popup menu.


Many of the shapes will have a line and a fill, and you almost never need both. Remove unnecessary lines; I set the lines of latitude and longitude to white, and eliminated the black box around the whole map. I selected the lakes and made their line and fill the same 15% Black as the ocean, then changed the rivers to make them blend in with the land (so they don’t show up, but don’t leave gaps). The countries now have a 60% stroke and fill; turning off the stroke left some gaps along state borders, so I just set it to the same color as the fill. I deleted the placenames, and changed the color of the coastlines to 60% Black again.


It’s perfectly possible to simplify things further, of course. Feel free to eliminate lines and labels and fade back land and sea as required to make your point. To crop away parts of the map you don’t want, draw a box over the desired portion (this needs to be the topmost object), select everything, then choose Crop from the cropmap.gifPathfinder palette. This will trim away everything outside the boundaries of the topmost object. (Remember to save a backup version!) For the map below, I’ve added a colored shape with a Gaussian blur, and used the Brush tool with the Arrows brush library to draw the currents. Clicking on an arrow with the text tool turns it into a path for labels to march along.


You can now use Save As to create an EPS for print publication, or Save For Web if you want a GIF or JPEG (the former is probably a better choice with maps) for PowerPoint or the Web. Remember, if you’re using color make sure it’s CMYK if the map’s for print, RGB if it’s for a computer screen (another reason why we save multiple versions…) There’s plenty more we could say about map editing, so feel free to mail me tips or queries, or comment below.