Let's build a map!
If you spend any time working in oil and gas in this province then you’re going to run into a situation where you need to put some stuff on a map. If you’re like me that involves complaining about it on twitter
I don’t know how I get myself into working with GIS data. I seriously have no idea.
“” Simon Timms (@stimms) April 28, 2014
The problem is that GIS stuff is way harder than it looks on the surface. Maybe not timezone hard but still really hard. Most of it comes from the fact that we live on some sort of roughly spherical thing. If we live in flatland mapping would be trivial. As it stands we need to use crazy projections to map a 3D world onto a 2D piece of paper
There are literally hundreds of projections out there which stress different things. Add to that a variety of coordinate systems which can be layered on top of it. There is the latitude/longitude system with which we’re all familiar but there are also a bunch of others. In Western Canadathe important one is the Dominion Land Survey(well most of Western Canada, we’ll get to that). The Dominion Land Survey was actually a series of surveys starting as far back as the 1870s. Bands of bearded men (there may have been bearded women too, everybody back then had beards) traveled around Canada plunking down lines to divide the land into 1sq mile sections called, well, sections. Why miles? Because of some guys calledJ. S. Dennis and William McDougall figured that a lot of people would be coming up from the states and would better understand miles. Thanks for screwing us over, again, with your stupid outdated measurement system, United States.
Anyway you can read a ton more about the system over atwikipedia. The important thing to know is that Western Canada is divided into 6 mile by 6 mile blocks know as townships and that these are divided into 36 sections and each section is divided into 4 quarter sections. Sections can also be divided into 16 legal subdivisions commonly known as LSDs. The LSDsare numbered in the stupidest way possible starting in the bottom right corner and counting up by going left and then up then pretending that we’re a snake and just flipping back and forward
The point of all of this is that LSDs are super important in the oil and gas industry because that is how you lease land. The result is that people want to see LSDs on their maps and, as seems to frequently happen, I got the task of building a map. This post is about how to get LSDs onto a map and show it to your clients who aren’t asses. Mostly.
The company for which I’m working has most of its interests in Saskatchewan, Alberta and BC. I started with Saskatchewanas I figured that I might as well get into thinking like a cartographer and working right to left straight off the bat(I hear that cartographers from Arabic countries work from left to right to maximize the confusion). The first step was to find some LSD data. Saskatchewan have an open data portal at http://opendatask.ca/data/which contains a link for LSD data. What you want in particular is theSaskGrid2012. This file contains a lot of stuff but the four things you want are the various high level map structures: township, section, quarter section and legal sub division. We probably don’t need quarter section as once we get to that level most people are interested in LSDs. Inside one of these zip files are a number of files which, as it turns out, are Esri shape files. Esri is a piece of GIS software. It is expensive. However there is a free alternative which has all the functionality we need along with 9000 pieces of functionality we don’t:QGIS. If you download and install this software it will let you take a look at the shape files. You can add it by clicking on “Add Vector Layer” then pointing it at the .shp file.If you load the township file it will get you something which looks like very much likeSaskatchewan. What’s more is that if you click on the little identify featuretool then on the map it will tell you the name of that township. Awesome!
For each township there are 36 section (6Ã—6) and for each section there are 16 (4Ã—4) LSDs. So for Saskatchewan there are something like 7000 townships, 250 000 section and a mind blowing 4 million LSDs. Quite a bit of data.
So now we have a map. But it only works inside of QGIS and I’m sure not going to go around supporting that. It would be really nice if this layer was available on a Google maps like thing.
Leaflet.js is a nifty library for manipulating maps. It can use any number of map backends but I usedOpenStreeMap because it is awesome. Like really awesome. Start a new ASP.net project and then go and grab the latest leaflet from theirsite. Leaflet is in nuget but it is an older version which hasn’t been updated for 6 months or so. Add the files to the site bundles in BundleConfig.cs. I also included my site files in this bundle for convenience
I created a typescript file for the home page based on the example on the lealflet home page
This can be used to select the intersecting polygons by doing
STIntersects will check the number of intersection points between the given polygon and the ones in the database. If there are any intersections then we have a match and we add that to the result set. Actually building the search area can be a pain as you actually build a geometry like so
This provides a set of data to return to the client.
We’re almost there, folks, thanks for staying with it. The last step is to get the returned data plotted on the map. This is simply done by adding the polygons to a multipolygon layer
That’s it folks! You now have a map which looks like
The labels are a bit jaggedy right now as I’m just using the envelope center to calculate the position of the label. It doesn’t take a whole lot to screw that up. Putting them in the top left corner helps with that a lot
P.S. I promised I would get back to BC’s system. They don’t use the DLS they use theNational Topographic System