7. Blue is for Water

This may seem obvious. However, sometimes in the heat of a design binge, it’s easy to select blue as a nice, neutral color to use on your base map.

Don’t do it!

Brains don’t like it. Namely, your map users’ brains.

Whether it’s right or wrong, your brain instantly equates blue on maps with water. Not just your brain — nearly everyone’s! Red is hot and fire. Blue is cool and water.

Context Disclaimer

Unless… You’re mapping Israel for an Israeli or Middle East audience.

In Israel, blue is often used to represent state territory and green is used to represent Palestinian territories and Arab-states (see below).

Israel Can Be Blue
In this case, and given the proper audience, blue might just work. Wouldn’t work for a generic US audience, though.

So why is this one of but 100 design tips? Because I still see GIS professionals use blue for their base maps. Frequently in simple reference or non-choropleth thematic maps. And it is an easy to avoid mistake.

Here’s an example: What are you looking at here?

Map of Greece
Sure, eventually you can figure out its the lower Balkans and Turkey. But your brain had to do a double-take. By default it presumes blue is water. As far as your brain is concerned, this map is speaking Greek.

Using blue to map land unnecessarily increases map complexity and map user cognitive load. In layperson English? Your brain only has so much processing power, and by mapping land in blue, you’re wasting your map readers’ attention and computing capacity.

Even with stat borderlines included, blue is distracting and your initial thought remains that it represents water.

Balkan countries
Still the Balkans. This time with country boundaries. My brain still wants the blue to be water. The boundaries actually make my brain work harder trying to resolve the issue — it makes even less sense that boundaries are being shown in the water… or wait… land… what?! Ahhh… my brain hurts.

Blue not only looks wrong. It doesn’t compute. Map users have to continually override their built in knowledge schema using a feedback loop: blue equals water, wait… no it doesn’t.

Using blue for land masses wastes energy. Be environmentally friendly — don’t waste your map users’ resources.


Looking for a Base Map Color Other Than White? 

When in doubt, choose light gray. Light gray is very neutral. It allows any color to pop in the visual hierarchy. People now associate it with shaded relief and land more readily than anything else, and… well, it doesn’t confuse people. Gray is as close to a blank slate as you can get besides white.

Whereas the color white may inadvertently imply no data, nada, zilch, nothing. Gray doesn’t suffer from this shortcoming. Gray let’s a map user know that a cartographer intentionally picked a neutral color. It’s not a mistake. It’s not forgotten space. It’s been noticed.