Back in high school I had this idea for a field trip in a van. It was going to be what I did after college (where I would, of course, double-major in theatre and history), and it went more or less like this: most public schools these days have trouble getting the resources (time, money, manpower) for field trips, but field trips to historic sites were some of the best times for me as a kid, because you got to be where the past happened. ((In the words of one of the kids Sheri took on a house tour, you get to “touch history”)) In order to bring that experience to schools, I was going to get a van and fill it up with objects, clothing, and build a whole educational workshop that could go for a class period or half day in whatever space was available.

One of the features that I concocted was a map mash-up which would help students see the historic landscape and the modern simultaneously. There would be a map, probably the historic map, printed large so everyone could see; the other map, say the modern street map, would be printed on overhead projector type clear plastic so it could overlay the historic one. I thought the visual collision of past and present would help other kids see how history is related to the world around us, in the roads and fields and buildings.

Needless to say, I never got around to making the field trip in a van, but the map idea stuck with me. Which is why I really enjoyed a number of the sites on the syllabus for this week (11), which are using digital tools to make a much more sophisticated version of a historic/modern map mash-up. Hypercities is only currently configured for select cities, but the interface is good. It allows users to select a time range and to increase or decrease the opacity of the historic map(s) which overlay a modern satellite view.  Some of the cities have only a few maps; London apparently only has one, but it’s John Snow’s cholera map!

Map overlays or mash-ups aren’t, of course, the only sort of visualizations available for historians. The variety adds to the use, and I find visualization tools personally useful. I am the sort of person who makes mind maps, writes and reads simple entity-relationship diagrams for relational databases, and appreciates a good flow chart.

However, when I remember my high school plan and impulse, I look at the visualization tools another way. Visualization tools can help a historian analyze their data, but they can also make that data more comprehensible to an audience, whether scholarly peers, students, or the public. It could be in the form of an argument, where the visualization illuminates an aspect of the data which is otherwise buried. It can also be in support of an argument, for example a relational diagram which highlights what aspects and relationships were considered most important in the data.

For this second form of visualization, the trick is making something which is true to the data and comprehensible to the reader. Even my low-tech overhead sheet map wouldn’t work for a group of students who had no idea how to read a map. Provide a key, define your terms. A visualization may be gorgeous, but if you’re the only one who can understand it, what’s the point?