What Are Some Other Coordinate Systems?

WE USE OTHER SYSTEMS, besides latitude and longitude, to describe location. These include the Universal Transverse Mercator (UTM) system, the State Plane Coordinate System (SPCS), and the Public Land Survey System (PLSS). Each is very useful for certain applications, and some are used to specify the location of real-estate properties appearing on legal documents associated with purchasing a house. Therefore, they are relevant to most citizens, even those who are not geographers.

How Do We Use the UTM System?

Maps can show large regions, even the entire world. The main considerations for displaying large regions arise mostly from the fact that we live on a three-dimensional world (a sphere) and flat maps are two-dimensional. One solution to this challenge is the Universal Transverse Mercator (UTM) system, a method of identifying locations across the nonpolar part of the Earth. UTM is the most useful method of location for people who frequently hike or camp, or for people, like forest rangers and wildlife researchers, who work outdoors in nonurban settings.

1. The UTM system slices the nonpolar region of Earth into 60 north-south zones, each 6° of longitude wide. The slices are numbered from 1 to 60, with numbers increasing eastward from the International Date Line. A slice comprises two UTM zones, one in the Northern Hemisphere and another in the Southern Hemisphere. For example, most of Florida is in UTM zone 17 N, whereas the southern tip of South America is mostly in UTM Zone 19 S. What is the UTM zone for the place where you grew up or go to school?

2. The slices are further subdivided into grid zones, each 20° of latitude long, as shown by the rectangles on this map. The purpose of UTM zones is to ensure that location is accurately portrayed in the middle of each division, with the understanding that there will be increasing distortion away from the middle. Due to large distortions that occur in the UTM system near the poles, UTMs are typically only used between 80° N and 80° S latitudes (we do not use UTM within 10° of the poles).


3. For a location within a grid zone, we specify coordinates as eastings and northings. Eastings are a measure of the number of meters east or west of the central meridian for that zone. Northings are a measure of the position north or south of the equator. The map below shows the aerial photograph of the horse and cow pasture shown earlier in this chapter, but this time with a UTM grid labeled with eastings (along the bottom of the map) and northings (along the left side of the map).

NGA-Office of GEOINT Sciences

4. The advantage of the UTM system is that it is a “square” grid system measured in meters rather than degrees, so it is convenient for measuring direction and distance. Note how useful this grid and UTM system would be if you were riding around trying to record the location of each horse in the pasture. Two horses (not visible here) are grazing at an easting of 495250 and a northing of 4214100; can you determine about where these horses are? Are they in the pasture?

5. We can specify locations using several systems, and convert from one location system to another. The map above shows the position of a site expressed in both latitude-longitude (commonly called “lat-lon”) and UTM coordinates. There are Internet sites that allow easy conversion from lat-lon to UTM and vice versa. To go from UTM to lat-lon, you have to specify the UTM zone, which can be determined using the large map near the top of this page.

How Do We Describe Locations Using the State Plane Coordinate System?

The State Plane Coordinate System (SPCS) is a third system for mapping, used only in the U.S. Its name derives from the system ignoring the curvature of the Earth, treating the surface as a “plane,” and being based on a reference frame that is optimized for each state. As a result, the system can use X-Y coordinates to represent positions, simplifying land surveys and calculations of distances and areas. Another advantage is that the projection was chosen based on the geographic orientation of the state or section of the state, to minimize distortion for that area.

In the SPCS, most states are subdivided into two or more zones called state plane zones; some states are a single zone. Alaska has 10 zones and Hawaii has five zones. The boundaries of the zones generally are east-west or north-south, but are not straight, following local county boundaries (trying to keep a county within a single zone).

How Do We Describe Locations Using the State Plane Coordinate System?

States that are elongated east-west, such as Tennessee, use different map approaches to generate the state plane coordinates than states like Illinois that are elongated north-south. The goal is to customize the drawing of the map so as to minimize the distortion that is always present when trying to show features of a spherical Earth on a flat piece of paper. So local U.S. maps, such as for flood zones, roads, or property delineation are likely to use the SPCS. If you buy a house in the U.S., the legal documents will likely use SPCS to specify the location of the property, perhaps accompanied by a survey in UTM.

How Do We Describe Location Using the Public Land Survey System?

The Public Land Survey System (PLSS) is another system used in the U.S. for describing the location of lands and for subdividing larger land parcels into smaller ones. When you hear someone refer to a “section of land” or a “quartersection,” they are talking about PLSS. The PLSS is also called the township-range system because these terms are used to describe areas of land.

States Included in the PLSS

The Public Land Survey System was designed specifically for public lands, such as those administered by the U.S. Department of the Interior, and as a result is most widely used in states where there are federal lands. It is not used in many eastern states, where there is little land that is not privately owned, and in Texas, which has much state-owned land.

PLSS is defined for different regions, in each based around some initial point. From this point, a Principal Meridian extends both north and south and a Base Line extends both east and west. Beginning at the Principal Meridian, the land is subdivided into six-mile-wide, north-south strips of land called ranges. Beginning at the Base Line, the land is subdivided into six-mile-wide, east-west strips of land called townships.

Each square of the township-range grid generally is six miles in an east-west direction and six miles in a northsouth direction, so it is 36 mi2 in area. Each grid square is further subdivided into 36 sections that are each one square mile in area. Township and range lines and section boundaries are included on many topographic maps.

How Do We Describe Location Using the Public Land Survey System?

Each one-square-mile section can be further divided into quarters, eighths, and even smaller subdivisions. The rectangle in the southeastern corner of Section 14 would be described as being in the eastern half of the southeast quarter of Section 14, Township 2 South and Range 3 East. This is abbreviated: E1/2 SE1/4, S. 14, T2S, R3E.