Maps and Me, A Sordid Love Affair

As long as I can remember I've been fascinated with maps. Travel as well, but especially maps. My friends and I used to play role playing games (never Dungeons and Dragons specifically, but similar ones), and at one point I got a huge sheet of paper to be able to map out a big fantasy world we could use for our games.

These days I'm more interested in making maps of the real world. I currently use a free program called MICRODEM, which I'd originally downloaded to convert satellite images to maps for the game Transport Tycoon... but that's a different story altogether. The maps I've been making use shapefiles showing various census and administrative divisions in Canada and the US, and census data.

The current fling started because I wanted to map out population density on both sides of the Canada/US border, covering Montréal, Québec (city) and the adjacent parts of New York and New England. The idea was to get a real image of how the population is laid out on both sides of the border, but not actually plotting the border as a line across the map.

I looked all over the place and never once managed to find anything like it. Most maps I found were either exclusively of the US or exclusively of Canada, or didn't really have the level of detail I was looking for.

So I made this.


(Click to enlarge)

The colour scale maxes out at 100 inhabitants per square kilometre on purpose. I wanted to make sure that sparsely populated rural areas, and the slight differences between them, would show up. The side effect of this is that even smallish cities like Burlington, Vermont (the larger of the two dark spots south of Montréal) seem bigger than they really are, because the black can represent 101 people per square kilometre, or 4000 people per square kilometre.

One issue was getting a hold of comparable data on both sides. The issue of metric vs. imperial units (people per square kilometre in Canada, and people per square mile in the US) was easy enough to get past by converting the US data to metric. But it was a little more difficult to get data broken down into similarly-sized parcels of land on both sides. In the US, I ended up using Census County Subdivisions, which are somewhat regular in size. In Canada I used Census Subdivisions, which vary quite a bit in size, as they sometimes correspond exactly with the limits of a municipality, and other times correspond to a non-governmental découpage of rural territory.

Data used
From Statistics Canada / Statistique Canada,
Census Subdivision Boundary Files and Population and dwelling counts, both for the 2006 census.
From the U.S. Census bureau, Cartographic Boundary Files of Census 2000 County Subdivisions and population density by census county subdivision from the oh-so-user-friendly American FactFinder... To repeat what I did, simply go to Data Sets, Decennial Census, 2000 Census Summary File 1, Geographic Comparison Tables, select "State", select a state, select "Place and (in selected states) County Subdivision", include data from the group "GCT-PH1-R.", view and download it.

Linking the data and maps
Canadian census boundary files can be linked to the data through the Geographic Code / CSDUID, which is a unique ID that should match perfectly 1-to-1 in both files for the same census year.
US census data files contain a field called "place" which will contain something like "Bridgeport town, Fairfield County". Truncate off the county, and you will have something you can compare to the two fields named "NAME" and "LSAD_TRAN" and that will contain "Bridgeport" and "town" respectively. Watch out for some of the overlapping data areas in the data file -- cities split across two counties and recorded once as a city, then twice as city areas in each of the two counties, etc. Also in some larger states like New York, there are cities with exactly the same name in two counties, so the county info can't just be thrown away as with smaller states.

(You bored yet?)

The end result is pretty different from what I expected. In my mind, the border had a big effect on population density. Northern New York and Vermont feel so desolate in comparison to the area of Québec just on the other side of the border, that I was really expecting to see the border through the difference in population density. But while you can indeed make out where the border is because the divisions on either side of it don't line up, the population density on both sides is quite similar. You can almost make out a corridor of lightly-populated areas that run uninterrupted from Montréal to Plattsburgh, NY and Burlington, VT.

If you stand back and stare blankly at the map from a distance, a 3-D dinosaur also pops out at you.