A Concurrent Session on GIS

Last week I attended an excellent session at Sweet Briar on GIS for Biologists, and what I saw and heard there has influenced what I want to explore here. I am a long-time beginner with GIS --long-time because I've been thinking about computer mapping for about 30 years, and have played with it in various forms, including line-printer maps (SYMAP), CAD (AutoCAD, in an early incarnation of the product) and, during the last year, ArcView. I'm entirely self-taught, which means that I've learned bits and pieces as I needed them, and also means that I have blind spots about a lot of features and possibilities that people with real training would consider obvious. But I have this long-run conviction that spatial distribution is a vital pedagogical and research perspective for many of the fields I've been professionally involved in as an anthropologist (and soi disant human geographer, ethnomusicologist, and ecologist), and now as science librarian. Simply put, we are awash in spatial data from remote sensing sources, data applicable to the interests of many of the sciences and to disciplines outside the sciences as well. Indeed, many of these data are of transdisciplinary interest and relevance. We have to learn --and to teach-- effective ways of analyzing these data and presenting the stories they tell. And desktop GIS packages like ArcView realize the possibility of the sorts of exploration and analysis we need to develop.

So where do we get the maps in the first place? Lots are available on the web, in various formats. And maps can be digitized in various ways. And various forms of images can be used as layers upon which new layers can be drawn. So, for example, geoTIFF images are available for topographic quads (the one for Lexington is \miley\gis\vfic\O37079g4.tif)

I want to offer a pretty simple example, whose greatest advantage is that the maps we can make are inherently meaningful to us --we can look at patterns and start to interpret and explain them. We'll use a readily-available (downloadable via the web) dataset on agriculture in continental US counties (it's in \miley\gis\vfic). Look at this for a few minutes:

Even without knowing what data are mapped, we can immediately start to interpret the image:

As a matter of fact, the map shows "Percentage of county as soybeans for beans, harvested, 1987" (the variable's name is 'pct2307').

Here's an image of some of the data that lie behind the image:

So what we're seeing is an association between a .dbf file (manipulatable via any spreadsheet program) and units (county boundaries) represented in Cartesian space --in this case, we're looking at a surface [% soybean area] approximated with vector data.

The simple point here: we can make all sorts of maps by assigning values to predefined units. If we had other data for U.S. counties we could import those data and show them; if we wanted to manipulate the data via the spreadsheet, we could show the results as new maps. No big deal, unless you try to do the same thing by hand.

So we need a guide to the available variables of the U.S. agriculture database, so that you can try out some of them yourselves.

But first we'll need to document some of the basic moves for using ArcView. I want to keep these simple, since the object here isn't to teach the use of ArcView, but to let you try out some of the basic features. Once ArcView is running (it's on the START menu on the lab machines)

  1. click on the New button to open a View
  2. Find the button just below Edit that has a + sign on it --the Add Theme button, click it, and navigate to P:\GIS\VFIC. You'll see 5 'feature data sources' open. Double-click any one of them to open it.
  3. click in the upper-left-hand box of the View1 window to display the base map
  4. double-click on the colored rectangle to Edit the Legend
  5. choose 'Graduated color' from the pulldown Legend Type menu
  6. use the Classification Field pulldown to select [by clicking once] one of the NUMBERED variables for display (see the list to translate their cryptic numbering...)
  7. click the Apply button to see the variable mapped.
  8. try other variables, use the Classify... button to change the number of classes
  9. and/or try adding other themes