4h.
The Universal Transverse Mercator (UTM) Projection

 

Our discussion concludes with a description of one of the most widely used projections for localized mapping of smaller regions. This system employs a Cartesian grid of coordinates. This UTM projection system is used for Canadian Topographic maps, and is very commonly used for digital GIS data of local regions. You will encounter data that is projected in UTM quite frequently.

The UTM projection is actually a composite projection, comprised of 120 individual projections (2 for each zone). For the UTM projection, the Earth is divided into 60 longitudinal zones, each of which is 6 degrees of longitude wide (see Figure 1). Each zone covers the Earth from 80o S to 84o N (the Polar Regions are mapped separately. See the section on the Universal Polar Stereographic Projections below). For the northern and southern hemisphere each individual 6 degree zone, a transverse secant Mercator projection is made, centered on the central meridian of that zone (Figure 2).

Figure 1. UTM Zones Globe.

 

Figure 2. Universe Transverse Mercator Cylinder.

Figure 2. Universe Transverse Mercator Cylinder.

Because the projection is secant, the cylindrical developable surface slices through the generating globe. This creates two standard lines that run north/south through the zone on either side of the central meridian for that zone. This produces a band of low distortion that runs north/south through the entire length of the zone.

As seen in Figure 3, the UTM longitudinal zones are numbered from 1 to 60, starting at 180o W and moving eastward. Each longitudinal zone is divided in 8 degree latitudinal bands, designated by letters starting with band C (starting at 80o S) and ending with band X (ending at 84o N). The letters I and O are omitted from this lettering to avoid any confusion with zone numbers. For example, we could say that Waterloo, ON is located in UTM zone 17T. Canada is covered by zones 7 to 22. 

Figure 3. Military Grid Reference System (MGRS).

UTM Cartesian Grid references

For each hemisphere of each UTM zone, a Cartesian grid is established, based on a false origin point for that half of the zone. The false origin has the coordinates 0,0 and is located so that the entire zone falls in Quadrant I (with positive X and positive Y values).

For the northern hemisphere of the zone, the false origin is located on the equator, 500,000 m west of the central meridian for the zone.

For the southern hemisphere of the zone, the false origin is located 10,000,000 m south of the equator, and 500,000 m west of the central meridian for the zone see Figure 4. 

Figure 4. False Origin Locations for a UTM Zone (a) and the UPS Zones (b).
Figure 4. False Origin Locations for a UTM Zone (a) and the UPS Zones (b).

With the false origin points established, we can now locate any feature in that zone by providing its Easting and Northing coordinates. The Easting coordinate is the X coordinate, and the Northing coordinate is the Y coordinate. For example, the Environment 1 building on the UW campus has UTM coordinates that are approximately 17 N 537000mE, 4812700mN. This means that the EV1 building is located in zone 17 North, with coordinates 537,000 metres east and 4,812,700 metres north of the false origin for the northern hemisphere of zone 17.

A UTM grid is shown on Canadian topographic maps. A 1 km grid is shown on the maps at the 1:25,000 and 1:50,000 scales. A 10 km grid is shown on the 1:250,000 scale maps. UTM coordinates are shown in the margin of Canadian topographic maps, allowing you to determine the approximate location of features on the map. A guide is provided on the map to explain how this is done.

The Universal Polar Stereographic Projections (UPS)

The 60 longitudinal zones used in the UTM projection cover the latitudes from 80o S to 84o N. This ensures that the zones cover the major continents of the Earth, from the Southern Ocean to a point North of Greenland. The North and South Polar Regions are covered by two secant stereographic projections, known as the Universal Polar Stereographic projections. Each of these UPS projections has its own Cartesian coordinate system, with a false origin as shown in Figure 4.