The best data or analysis in the world will have a hard time being effective if it can't be presented effectively. There are two elements to communicating with GIS - designing the overall product, and applying effective cartography to the map itself. 

COMMUNICATION AND DESIGN

Almost all maps include a "frame" design (titles, color bars, etc.) as well as an actual geographic picture - some may also include narrative text, charts, graphs, etc.  Use these principles to give your "map products" careful design so that they achieve your overall intent.

1.  Begin by defining your purpose and your audience:  All maps are selective - they show what their maker intends.  Have a clear objective and message in mind when you go to produce your map. Even if it is very technical, work out what you want the viewer to remember most. Then ask, who will see this map product and under what circumstances? Will it mainly be used in a small working group, handed out as a flyer at public meetings, or used as a backdrop for a press conference?  Is the audience technically knowledgeable?  Be specific about the type and number of people who most matter to your project.  Common pitfalls:  assuming that your map just shows "data" rather than having a message;  or, developing a map for your own taste, rather than understanding what your audience needs.

2.  Make your map a story:  Design a map product that takes the reader on a journey.  Unfold your messages in layers, not all at once. As the viewer looks more closely, additional information beyond your primary message should emerge. Don’t force the viewer to read this information when they first see the map. Look at newspaper front pages for examples of how to combine graphic elements in an overall story.   Common pitfall: use all the same size and color fonts for title and map labels.

3.  Keep it simple:  A map should have one primary message that is instantly clear to most people who see it – show your map to someone who has never seen it and ask them to tell you what it says five seconds after they look at it.  Remove all information from the map that is not essential.  Common pitfall: drawing attention first to a utility element such as a large or centrally placed scale bar or north arrow, or an overlarge legend; or, hiding the title in small fonts.

4. Direct the viewer’s eye:  The frame of your map (title, graphics, legend, etc.) should integrate with your map to draw the viewer’s eye to your messages in order of importance.  Again, have someone look at it from the map’s intended viewing distance and tell you what draws their eye in the first few seconds, then when they look a bit longer, etc. Use your strongest colors for the most important features.  Common pitfall: making lakes and other background water features a very rich and dark royal blue, which will dominate the viewer’s perception.

5.  Design for a viewing distance:  Every map has an optimal viewing distance. For a page map, it may be only a foot or two; for a large poster it could be 10 feet or more.  Place your map at its intended viewing distance and assess its impact.  Common pitfall: reviewing a poster map only from a foot or two viewing distance, which prevents seeing larger patterns in the full map.

Use these principles to judge the effectiveness of your map – and compare others’ maps to see what works and doesn’t.

CARTOGRAPHY

Cartography deals with the design of maps themselves. There are many good resources for improving your map design - among the best are:

Designing Better Maps: A Guide for GIS Users
by Cynthia A. Brewer  ESRI Press, 2005, 220 pp - published by ESRI Press, this comprehensive book is a complete guide to a wide range of design techniques.

Making Maps : A Visual Guide to Map Design for GIS   
by John Krygier and Denis Wood   2005    This book is equally useful, but focuses more on the concepts of design. It is less a technical cartography guide than a tour of effective map communication strategies. Purchase from Amazon.com

Other good web resources include:

GIS Lounge Cartography site

North American Cartographic Information Society (NACIS)

Cartographic Communication Notes - Univ. Colorado faculty site, with an eclectic and useful array of guidelines

The Map Room - a great blog about mapping

Color Brewer and ColorBlender – useful tools for choosing colors that work well together in map design and cartography

Relief Shading website - for those who want to explore how to create beautiful elevation shading in their maps

Making Maps Easy to Read – A somewhat technical site in the UK that has a variety of good tutorials

ESRI Map Gallery – see this online gallery of users' maps

Communication Arts Magazine – go to Interactive Design Annual

Perry-Castenada Map Library at Univ. Texas - excellent online resource of a wide range of maps.  

David Rumsey Map Collection, a remarkable online collection of over 10,000 maps from the 1700s to 1900s. – 

 
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