Can’t make sense of (UTM?) boundaries coordinates from Statistics Canada

boundariescanadautm

I downloaded a GML file of cities boundaries from Statistics Canada, but I can't make sense of them. For example, when looking at the boundaries for a city north of Toronto (Markham), the first coordinate pair in the list (gml:posList tag) is 7232029.8171445 964392.282857482.

It looks like the coordinates are in UTM format, but when I plug the numbers into a converter online to see them in long/lat using NAD83 and zone 17, it points to somewhere in the middle of the Atlantic Ocean.

The coordinates are accompanied by a PDF file that specifies the following geographic representation, but it still doesn't seem to help. I tried subtracting the false easting and northing values, but that doesn't result in proper coordinates.

Projection: Lambert conformal conic
False easting: 6200000.000000
False northing: 3000000.000000
Central meridian: -91.866667
Standard parallel 1: 49.000000
Standard parallel 2: 77.000000
Latitude of origin: 63.390675
Linear unit: metre (1.000000)
Datum: North American 1983 (NAD83)
Prime meridian: Greenwich
Angular unit: degree
Spheroid: GRS 1980

If anyone can provide some help on how to properly convert these numbers to long/lat it would be very helpful. I want to overlay them on a map in a custom application, so I can't just get the data in another format that's compatible with specific GIS apps.

Best Answer

The numeric values you are seeing are map coordinates but not UTM. The information you shared identifies the projection as Lambert conformal conic. This is EPSG:3347, known in QGIS as NAD83 / Statistics Canada Lambert.

Also documented on spatialreference.org

Related Solutions

[GIS] Creating/generating LDU polygon boundaries of Canada

REGARDING IMPLEMENTATION OF POLYGON STORAGE

To implement the concept of georeferenced polygons one must to establish the geopoints that serve as vortices (line endpoints) around the polygon (on the perimeter / path / track) and save them in order, repeating the first geopoint at the end to close the polygon.

One critical decision in mapmaking is determining what parsing format will be used to store geodata (kml, txt, gpx, for example). Some apps render many of these formats, others only a few, some export to various formats, other only to one or two of them.

I very much like GPS Trackmaker as a free conversion / mapping / downloading tool. Their premium solution is great, too.

In this case, i chose TXT files because they are very readable, though they offer infinitely less features and control than, say, kml.

If you examine a polygon parsed for TXT map rendering, you will find something like:

Datum,WGS84,WGS84,0,0,0,0,0
TP,D,-22.825397,-50.153163,00/00/00,00:00:00,0,1
TP,D,-22.825200,-50.152714,00/00/00,00:00:00,0,0
TP,D,-22.823723,-50.153354,00/00/00,00:00:00,0,0
TP,D,-22.822100,-50.154057,00/00/00,00:00:00,0,0
TP,D,-22.821690,-50.161636,00/00/00,00:00:00,0,0
TP,D,-22.826374,-50.161976,00/00/00,00:00:00,0,0
TP,D,-22.828237,-50.162113,00/00/00,00:00:00,0,0
TP,D,-22.828402,-50.161358,00/00/00,00:00:00,0,0
TP,D,-22.828742,-50.160024,00/00/00,00:00:00,0,0
TP,D,-22.829096,-50.158811,00/00/00,00:00:00,0,0
TP,D,-22.829479,-50.158032,00/00/00,00:00:00,0,0
TP,D,-22.829795,-50.157471,00/00/00,00:00:00,0,0
TP,D,-22.829857,-50.157399,00/00/00,00:00:00,0,0
TP,D,-22.827251,-50.157266,00/00/00,00:00:00,0,0
TP,D,-22.826972,-50.157094,00/00/00,00:00:00,0,0
TP,D,-22.826561,-50.156311,00/00/00,00:00:00,0,0
TP,D,-22.825397,-50.153163,00/00/00,00:00:00,0,0

notice that your first geopoint ends with 1 but all others end with 0. every new polygon starts with a 1. if your txt file comprises multiple polygons, it might read

... 
TP,D,-22.826972,-50.157094,00/00/00,00:00:00,0,0
TP,D,-22.826561,-50.156311,00/00/00,00:00:00,0,0
TP,D,-22.825397,-50.153163,00/00/00,00:00:00,0,0
TP,D,-22.8262790668339,-50.1473961808541,00/00/00,00:00:00,1
TP,D,-22.8253937791693,-50.1469750073087,00/00/00,00:00:00,0
TP,D,-22.8251435375745,-50.1460977703752,00/00/00,00:00:00,0
TP,D,-22.8249603671508,-50.1452553933599,00/00/00,00:00:00,0
TP,D,-22.8284303087316,-50.1438831245289,00/00/00,00:00:00,0
...

REGARDING HOW YOU OBTAIN THE DATA

I recommend that you request the info from the Canada Post directly. You will probably receive a list of street / road addresses, which will then have to be converted to geopoints. You might be able to get away with getting the data from a Google API, but it is certainly irregular and you don't want to have a commercially useless list of geopoints, do you?

So you probably use opensource / community developed Nominatim 's API and batch convert. Please read their terms of service, too!

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