G. P. S. BASICS

CHAPTER THREE The UTM Grid (Universal Transverse Mercator) The UTM grid is a metric grid system based on 60 grid zones around the globe and a set of values in meters from reference points of the grid. We are still working with the same basic components of a grid as we explained in Chapter 2 with a set of references, units of measurement, and some designation of direction from the references to clearly identify a position. Figure 12 Figure 12 pictures how these 60 zones look like around the globe. These zones are simply numbered 1 through 60 starting just east of the International Date Line and continuing easterly all the way around the globe. The zones are defined by meridians of longitude that are 6E apart. They don=t go all the way to the poles but only to around 84E North Latitude and 80E South latitude. The Poles are covered by a separate grid. Figure 13 shows how several of these zones would appear if they were flattened out. Notice that the lines of the grid do not all run parallel to the bordering meridians. They are only parallel to the meridian in the center of the grid which is called the Central Meridian. This Central Meridian is the vertical axis or reference line for each zone. The horizontal reference line for each zone is the equator, see Figure 14. For the areas in the Northern Hemisphere, the Equator is considered zero and everything above it is in meters North. For the Southern hemisphere, the equator, but it is given the value of 10,000,000 m North. Everything below the equator is measured in meters less than the 10,000,000 North. Page -17- The Central Meridian in each zone is designated as 500,000 meters. Everything east of this is greater than 500,000 meters and everything west of this is less than 500,000 meters. At the equator, each zone is almost 1 Million meters wide. It is important to understand that the reference point is not zero or 1 Million, but the Central Meridian at 500,000 meters. Figure 13 The meters Easting never gets to zero or to 1 Million. Any position is defined as meters Easting and meters Northing. The rule for reading UTM coordinates is to read right then up. There is also a Latitude Band Letter which is assigned to areas of latitude starting with the letter C way down at the bottom of the zone going up through N at the Equator continuing to letters X in northern Canada. North America in generally bands R,S,T,U and so on. Figure 14 Often your GPS receiver will not reference the Band Letter only Zone, and Meters Easting and Meters Northing. A typical coordinate that you might see on a GPS receiver would look like the one below: 12 59095E 3785889N This means that the location is in Zone 12 and is 59,095 meters Easting, and 3,785,899 meters Northing. Your map will have grid tick marks something like the ones for Lat/Long except the numbers are large so they often enlarge and bold numbers for the thousands of meters like this A0564000mE@ or A4728000mN@. It is a simple exercise to then use a scale that measures meters for that scale of map to measure meters East of a reference lineand North from a reference line to get the exact meters Easting and Northing for the coordinate. Page -18- Top Introduction | Contents | Chapter 1 | Chapter 2 | Chapter 3 | Glossary ©1997-2007 Waypoint Enterprises. All Rights Reserved If you surfed in, via search engine, etc., This is a remote page Please click the GPS Scale for our main index page.