Everybody knows that maps need a scale, a north arrow, and a legend. It’s reasonable advice, but there’s more to good maps. Here are 11 things you can do to make yours even better.
1. A scale is obligatory. That bit of the old advice was good. It’s a good idea to show the scale in a couple of different ways — perhaps coordinates (which also serve to show the location) and a scale bar. Make sure you include metres or kilometres — so that non-Americans can understand your map. Including some cultural features (towns, buildings, and so on) helps people intuitively tune in to the scale.
2. A north arrow is also obligatory. But the north arrow is not a substitute for showing the regional location and context of your map. Remember that most people assume north is at the top, so if it isn’t, make sure you make this especially clear.
3. Try to avoid needing a legend. Beware of making your reader look at the legend in order to decode every single map feature. Use standard symbols and colours whenever you can, and label other things directly whenever possible. If colours are available, use them to connect related features to each other and to their annotations or labels. If you are presenting a map digitally, give people a way to query the map layers directly, such as with mouse-overs, without cluttering the map itself.
4. Annotate the highlights. The spatial context the map provides will help your reader understand the story in your text. The most salient points of the map are probably obvious to you (see how the azimuth of fracturing changes so abruptly!) — help your reader get excited about them too. But don’t go overboard: if everything is highlighted, nothing is highlighted.
5. Show the database. It’s almost always a good idea to show the data that the map was generated from — wells, seismic lines, outcrops, and so on. This tells the reader which parts of the map are constrained by data, and which are interpolated by algorithms or concepts. You can show this information on a different visual ‘plane’ by using a semi-transparent grey layer.
6. Name the projection. If your map is a projection (that is, flat), then you must give the type of projection and the coordinate system you are using. Any time you publish or share spatial data, you must give the datum, even for geographic coordinates like latitudes and longitudes. Your data are useless without this information (see Location, location, location).
7. Learn more about colour. The biggest trap people fall into is using an overly colourful palette for their data, such as the classic rainbow colour scale. Such scales make the map hard to interpret, are hard for colour blind people to use, and leave very few colours for symbols and other annotation. There are plenty of better alternatives — read up on advice about colour, for example on the Rob Simmon’s Elegant Figures blog (ageo.co/18hYVY2) or Matteo Nicolli’s My Carta blog (mycarta.wordpress.com).
8. Present live data. Dropping screenshots into PowerPoint misses the point of working on computers. If the situation allows, you’ll make a better impression by showing your work live, so that it can be used as the powerful, flexible evidence it is. Your audience can ask questions, you can change scales any time, and you can interrogate your data live. (If the thought of this terrifies you, perhaps your story isn’t quite as convincing as you think?)
9. Appreciate good maps. Next time you’re reading a book or journal, notice which maps you find especially attractive or useful. Conversely, find your least favourite map, and list the things you don’t like about it.
10. Remember your reader. The point of your map is to inform, and to support your conclusions. Ask yourself — or better yet, ask other people — what they need to know from your map. Don’t clutter it with unnecessary details, and make certain the key data are clear and accurate. If the same map must serve two points, consider making the map twice, with different emphasis.
11. Be a good steward of your data. If your organization has a process for archiving map data, find out about it and use it. If they don’t, be consistent and rigorous, and encourage your colleagues to do the same. Shapefiles are the closest thing we have to a standard map format. When you publish, consider sharing your map data with others by attaching an open license and putting your files somewhere others can reach them — help make subsurface geoscience research more reproducible.
These tips are necessary but insufficient for producing great maps. Don’t forget you also need reliable data, sound geological modelling, and a clear idea of the evidence you wish to present. Those are the hard parts!