G-FAQ – What Makes a Good Map?
For this month's Geospatial Frequently Asked Question (G-FAQ), I extend the discussion started in the last edition on maps and spatial analysis. While it should be apparent from last month's G-FAQ that a map and spatial analysis are quite different, what is definitely not apparent is the basic question of what makes a 'good' map. Specifically, I will focus on this set of core questions for February's G-FAQ:
How does intent and audience come in to play when designing a 'good' map? How do I decide what elements to include on map? Are there any general recommendations that can be offered to create an effective map? What layers are crucial to include on a map?
Before we jump into this G-FAQ, let me quickly recap the definition of a map as used in our last edition:
A representation, usually on a plane surface, of all or part of the earth or some other body showing a group of features in terms of their relative size and position. (Norman Thrower, UCLA Geographer)
In order to build an effective map, I can offer the following set of recommendations. I have gathered this list of recommendations from both my professional experience and from cartography classes at leading US Geography Departments. While I believe these tips will help you design an effective map, by no means have I adhered to traditional cartographic approaches when I make these recommendations.
- The audience for and purpose of your map matters above all else.
- The first thing you need to consider when you create any map is the audience and its purpose. Your answers here will determine the elements, symbols, colors, text, formats, etc. you include in/use with the map. This tip is by far the most important I can offer for creating an effective map.
- The purpose of the map when combined with your audience will in part drive the final delivery format you chose. For example, if you intend the map for an audience that you only know from the digital world, then you will need to produce a digital map such as a PDF, JPEG, TIFF, etc. If you intend the map for an audience visiting a local museum, then you will likely use a printed format – unless they have moved to completely digital displays.
- How does 'audience' impact my map making decisions?
- There are two crucial considerations here. First, I consider the education/experience level of the audience. If I am making a map for a group of elementary school children, that has obvious impacts on my choice of colors, wording and symbols versus creating a map for a group of highly educated business professionals.
- Second, I consider the familiarity of the audience with the content in the map. When an audience is more familiar with the topic and/or geographic location, then you can eliminate map elements and data layers that might obscure the intent of your map. Simply put, the more your audience knows, the less information your maps needs to contain.
- How does 'purpose' impact my map making decisions?
- The purpose of your map helps to drive the complexity of the final product. If your map is educational in nature, then you will likely need a more complex final product with a detailed handling of map elements (see next month's G-FAQ for more info on this topic). If your map is for entertainment, then less complexity with 'fun' colors, labels and symbols is the direction you should head. While there are literally a million-and-one purposes a map can fill, it should be relatively intuitive how this will impact map complexity especially when combined with your target audience.
Decide on the final format and presentation of the map.
- Where will I publish this map?
What size will this map be printed out or displayed online?
- While there are a variety of formats your final map can take, most often you will be considering between printed and online. Each of these medium have their own considerations. Printed maps will be limited by the user's inability to zoom in (e.g. to see the tiny font you choose) so this in turn impacts your ability to display 'complexity.' An online map can be more complex as users can zoom in on them but you do need to have a clean presentation so that low resolution thumbnails look nice as well.
What color themes should I use?
- This helps to determine the complexity of the layers you can add to the map. The number of labels, map elements, etc. you can display grows as the size of your map does.
- Just as beauty is in the eye of the beholder, so too are choices in colors. Esri's ArcGIS offers a wide array of color choices that can be visually attractive. For a more 'scientific' approach to color choices (see Item ii below), you can check out Color Brewer. As always, limit the number of colors you choose to keep your map as simple as possible in its complexity!
- There are three basic types of variables that one can symbolize on a map: sequential, diverging and qualitative. Depending on the type of variable, your color theme should be structured accordingly. A sequential variable is one where the data is ordered from low to high, for instance the population of US counties. In this case, it's best to choose a color scheme with shades that progress from light to dark. Diverging variables emphasize a set of measurements as related to a median value, for instance comparing the average elevation of a county to the average elevation of the state. In this case, you would want two sets of colors with dark tones as the extreme and light tones as middle values. Qualitative variables are ones where the values are discrete categories, for instance the various types of roads in a city. In these cases, you want to choose colors with hues as different as possible. Color Brewer is a great site to help you determine the color scheme that is best for your set of variables.
- The images below will help to illustrate the importance of color themes and their ability to help display information effectively. In the final map, the goal is to show online viewers the different types of landmarks you can find in Boulder, Colorado. On this map, I displayed seven different types of landmarks against a dull grey background which does not confuse the other color choices. In the first example, I have used a range of blue tones as if the variable is sequential. When you look at the map, you will see how difficult it is to pick out one type of landmark from another. In the second example, I use a color theme that is designed for qualitative data, as that is the variable type we are dealing with here. In this example, you will instantly see how apparent the various classes of landmarks become.
What fonts should I use?
What symbols should I use?
- Just like colors are stylistic, so too is your choice of fonts. The basic division in fonts is serif (i.e. fonts like Times New Roman with 'little wings' at the ends of letters) versus san serif (i.e. fonts without the little wings as we use in this newsletter). While many claims are made about the legibility, professionalism and effectiveness of these categories of fonts, the science behind these claims is weak at best. In my opinion, pick one or two fonts that you like and that you feel portray the 'look and feel' of the map; and then use these fonts throughout the map.
In next month's edition of G-FAQ, I will finish off this discussion on the creation of an effective map with the three remaining tips that I can offer. Until next month, happy map making!
- There are only three basic types of symbols you can create: polygons for objects that cover large areas (lakes, forests, cities); lines for objects that are linear in nature (roads, railroads, streams); or points for objects that are a singular site (hospitals, police stations, parks). Scale can impact your choice of a polygon, point or line as if you are looking at a smaller geographic area, then a park might be better displayed as a polygon then as a point.
- As with the other items in this section, simple is better. Choose symbols that do a good job of illustrating your datasets. Often times, professional groups have a set of symbols that are considered 'accepted' – ArcGIS has a very large catalogue of them. Another great resource is using a Google images search to find maps on a similar theme to the one you are creating; and then examining the symbols they are using.
Do you have an idea for a future G-FAQ? If so, let me know by email at firstname.lastname@example.org.
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Brock Adam McCarty