Today we'll have a look at how to turn your map resources into electronic maps. For this, we'll need to additional equipment and resources wich we hope you will find useful. While we'd planned on visitting the SNRE site and using their digitizing tablets, due to problems with high-falutin' technology we're stuck here in our lab using old fashioned mouse digitization. No reason to cry over it, though: we can have fun anyway.
Lab Objectives:
When you get down to the tract level, you could consult the Census TIGER files to find the lat/longs of the centroids of the tracts (these too are available from the CIESIN site) - but this would be a lot of work. I'm sure that soon (if not already) some good soul will put a really good full address -> lat/long geocoder on the web. Right now this one is the best we've got!
Leah Estberg will help those needing or wanting help with scanning and/or OCR (Optical Character Recognition - useful for scanning in type-written data from dusty old books, say). We have reserved one of the scanners in the multimedia lab up in PHISA. Just because you scan an image or a map doesn't mean that you're obliged to use it in today's lab. I might suggest that you just use the images we've provided you for the lab, but if you have an equivalent theme (i.e. point or polygon) of your own and would rather work with that, fine.
If you're going to use the default images, download them to your space (from the browser) by right-clicking on the links to the images above - you'll be offered the option of saving the links as....
If you've zoomed so far that you can't see the whole image, then as you digitize, you may want to switch back and forth between the Draw Point button and the Pan button (the little hand icon), which allows you to move the image to new areas to digitize.
When you're done, run the statistics on the field, to make sure that you have a max, a mean, and a min of 1.
You can have a look at the data set in a different GIS (GRASS) via WebGIS, selecting the smallpox raster map, smallpox vector map, smallpox site map (choose a bright color for this map), and smallpox region. The vector map shows the Theissen polygons associated with the data as well, and that vector map was used to create the raster map.
I created this file because I was frustrated when I did exactly what you just did and couldn't figure out how to look at the coordinates of the points I created. They're stored in ESRI's proprietary shapefile, and I couldn't figure out how to get ArcView to show them to me. So I converted the shapefile to an Arc export file, then imported that into my favorite GIS, GRASS (which is free: public domain). I created the Theissen polygons, which again represent "Basins of control", if you will (also called voronoi diagrams), which are regions of space closest to the point contained in the middle of each region.
There are a couple of cluster statistics available from the WebGIS menu (look at the bottom of the page - click on Cluster Operations). At the bottom of the page which presents itself you will find a list of tests (we haven't talked about any of them yet). Choose one, select the smallpox site file, and then click on any point in the image. You will get a statistic calculated at that point. (We are in the process of adding all the tests which we will discuss in this course, so that people can try out the tests over the web. But enough of this! It doesn't have anything to do with digitizing.)
----- / / | . | \ --------(man, I wish I could find that icon image in some directory somewhere!).
Beware spurious rapid double clicks! That signals "all done". I try to consciously pause a bit between clicks as I move.
---------- /****/ / |****. . |****| \ -------------This cryptic symbol means that you're going to add an adjoining region. To do so, let's work on the 37/103 region next to the ND region. The strategy is to click inside the ND region, then click on a point where our new region will join the ND region (the northeast corner is good). Then click on the northwest corner, and descend the winding region edge, clicking as you go. If all goes well, you'll click all the way back to the first region. Go a little bit into the first region, double click, and the second region should magically appear.
Keep this up until your hand hurts, until time runs out, or until you run screaming from the lab shouting "I never want to see another mouse again as long as I live!": then quit.
This is the map and data set that was used for the BW join statistics example that you saw in your reading and lecture. If you finish this map, then you could create the BW map by adding a rate variable (derived from Population and Deaths), and coding by above and below the median. The neighbors can be obtained using the SPlus extension, but you take this on at great risk - two large, unweildy pieces of software trying to work together, yuck!
Page by Andy Long. Comments appreciated.
aelon@sph.umich.edu