GIS files are often organized based on the NTS maps grid. It is available in two standard scales, 1/50 000 and 1/250 000. The maps show a geographic grid (longitude and latitude) and a Universal Transverse Mercator (UTM) grid (kilometres). The area covered by a given map sheet is determined by its latitude and longitude. Since the National Topographic System uses a standard numbering system, knowing the map number allows you to quickly identify adjacent map sheets.
GIS files are often organized based on the ATS maps grid. The ATS is a grid network dividing the province into equal-sized parcels of land. Any parcel of land in Alberta can be located by its legal land description. Under the ATS, land is designated as being west of the 4th, 5th, or 6th Meridians (110°, 114°, 118° west longitude, respectively). More information.
The legal description of the section highlighted in the diagram above would be written as: 1 - 87 - 18 - W4 (Sec. Twp. Rge. Meridian)
Souce: Alberta Environment and Parks