# Category Archives: GIS

maps are just one way of looking at it

# free geodata for the numpty-about-Toronto

So if I want to learn some GIS skills, it would be helpful if I had some data to work with. Here are two data sources I have slight familiarity with:

toronto.ca | Open

Shapefiles, comprising:

The mixed map projections are a bit of a pain, and there are reports that some of the data is skewed from the rest of the Canadian data, but there’s much to love about this data.

An absolute tonne of data, in vector and raster formats. Services I’ve used are CanVec (vector data covering almost every feature) and Toporama (raster topographic maps; it has an associated Toporama Web Map Service).

# where am i?

My GPS just told me that the middle of the nearest road intersection to my house has the following coordinates:

lat=43.73066, lon=-79.26482

What does that mean? Since latitudes are positive north from the equator, and longitudes positive east of the prime meridian, that means I’m at 43.73066°N, 79.26482°W. This is what it looks like on a map:

If I wanted to put on airs, I’d quote the location in degrees, minutes and seconds of arc. These units are a bit fiddly to calculate (a minute being 1/60th of a degree, and a second 1/60th of a minute) but are traditional and compact. You can cheat, and put the location into Google Maps and it’ll spit out the DMS coordinates, or you can work it out:

```43.73066°N
43°
.73066 × 60 = 43.8396′
43′
.8396  × 60 = 50.376″
50″

79.26482°W
79°
.26482 × 60 = 15.8892′
15′
.8892  × 60 = 53.352″
53″
```

So, 43° 43′ 50″ N, 79° 15′ 53″ W it is. (I’ve used prime and double-prime characters as I think it looks neater, and it shouldn’t confuse smart quotes).

So that’s my location, relative to somewhere else. I guess one could take a theodolite sextant, learn how to use it, and see (roughly) how far north I am. Longitude’s tricky, and when I first visited Greenwich I really thought that they’d discovered the physical 0° meridian there, and how convenient was it that it was so close to London’s docks! (See, this blog’s not called Numpty’s Progress for nothing.)

But degrees don’t really tell me how far you are from something, and the surface of a not-quite sphere is inconvenient to map onto a flat surface. So from now on, I’m going to look around me as if my surroundings are flat.