Cartographer's Toolkit

For the most part, GIS map apps are inflicted on the public without user testing. User experience with the map app is also not studied after the fact, as a general rule. These things, which have the potential to affect thousands of people, are essentially designed and deployed in a black-hole environment where the best one can hope for is to get a few bits of feedback from colleagues on twitter or from a desk-mate who might simply state, “that’s cool.”

This is why I was excited to see the mention of a map application on a totally non-map related forum the other day and even more excited to see that there were a lot of responses regarding not only the content of the map but also regarding the usability of the map. What follows is a list I’ve made of what those responses consisted of, inasmuch as they provide instructive commentary for cartographers to apply to our mapping applications in general.

Our Case Study:

The map app

The forum discussion (non-mappers)

STATE THE DATA ORIGINS The mapping application has a 5 sentence paragraph defining how the mapped variable was calculated. This paragraph was also quoted in the original forum post. Even though the paragraph explained that the data was from a “Survey of Consumer Finances,” most people seemed to assume that the data was purely census data, based on the fact that census blocks were used as the geographic unit of display. A forum poster pointed out the source of the data later on in the discussion as people wondered how the census data was used to calculate net worth (it wasn’t.) Lesson: be clear about where the data comes from; people do want to know so don’t bury the information in a long paragraph.

SCRUTINIZE EVERY WORD The instruction to “click on the block” to see details about census data for that block was interpreted by at least one reader as “block” as in a 3d square object. Some readers were therefore not familiar with the census block concept. The lesson is that every word should be examined for alternate meanings, geographic differences, and level of reader knowledge about the subject. You don’t have to dumb it down to kindergarten reading level, but you do have to be cognizant of not using industry-specific terms for a general-public map.

ANTICIPATE AREAL UNIT SKEPTICISM Geographic units will be questioned by smart people. In this case, some people were unfamiliar with census block geography and wondered if the block polygons were always square, leading them to immediately wonder if there was a spatial bias. Of course geographers know there is always some kind of bias with spatial units. (They imply that things are more similar within than without as if there were hard edges between two adjacent units when in reality most data such as soils or census data is continuously distributed, is just one example of the problems inherent in geographic units.) But non-geographers don’t know about the modifiable areal unit problem. I think that there isn’t much a geo map app can do to acknowledge this bias other than with wordy disclaimers, but it remains a point to consider mentioning when you present the map in person.

CLICK-FOR-DATA NOT ALWAYS OBVIOUS A few people seemed to not realize that you could get at detailed information about the blocks by clicking on them. To describe how to do it one responder simply explained, “it shows up when you click on the colors.” The obvious to you is not always obvious to others. When explaining how to do something on a map app, you can make the wording quite simple, as was done here.

MAPS ARE FOR PONDERING Starting a conversation with the map and getting people to think about the data is a good end in itself. In this case there was a good discussion about whether the data reflected the net worth of renters or owners and how people with multiple homes were represented.

THEY ALWAYS WANT MORE DATA People will always want more specificity with data. In our example people were eager to know more specifically what the net worth was in places where it was listed as “$500,001,” which was actually just the top of the data range. While there may be very few census blocks with net worths higher than $500,000, finding those few census blocks (the extreme outliers) might be the most interesting thing about the map. The way in which a choropleth is broken down is therefore extremely important to think through thoroughly. For example, for this data and this use case, where outliers are important, the quantile method of class breaks is especially problematic.

ZOOM LEVEL AGGREGATION IS GOOD Several users noted their appreciation for zoom level based geographic aggregation. For example, census tract boundaries are shown at lower zooms while smaller census block boundaries are shown at higher zooms.

ETHICS MUST BE CONSIDERED The notion of data being scary when it isn’t aggregated–when it’s available at a household level, for example–was brought up. All map makers need to be aware of ethical practices. Map app philosophy, however, needs a Socrates for the profession, and until the time when we have an overriding philosophy we have to make conclusions on ethical practices on a case by case basis.

DISCLAIMER FOR THIS LIST Lastly, while reading through the forum comments about the map, be mindful that the majority of people who used the map might have had zero trouble using it, zero trouble mentally thinking through and overcoming geographic unit bias, and zero trouble with data privacy concerns. To adequately understand the spread of user reactions we’d have to do a real study. Thus the disclaimer: empirical data is instructive but use it with caution.