A good topographic map can save your life – or at the very least your outdoor adventure – providing you can interpret what it has to say. Here are six things you should know about topographic maps:
When you first open a topographic map – or any map for that matter – check the date it was printed. If the map in question is 25 years old, many of the details, particularly roads and trails, may have changed. Be sure that you use a recent map for your backcountry adventures.
Hold the map so that it points in the correct direction. Use your compass to find north if you don’t know where it is already and then align your map accordingly. On every map you’ll find a compass rose – a four-pointed cross that shows cardinal directions (north, south, east, west) – or a directional arrow pointing north.
- Key Facts
In one corner of the map, there is always a key that will help you identify map features – i.e. what’s the meaning of dashed lines versus dotted, blue lines versus black, solid squares versus circles, etc. Take a moment to familiarize yourself with these symbols.
Usually at the bottom of the map you will find a ratio scale. The most common scale used for U.S. Geological Survey (USGS) topographic maps is 1:24,000. It represents a scale of the distance on the map compared to the distance on the ground. The larger the number, the larger the area covered by that map. There is also a scale for distance which you can use to figure out approximately how far it is from point A to point B on the map.
Topographic maps use contour lines to show elevation above sea level. The elevation change between each line depends on the scale of the map. These intervals are set number. When the contours are widely spaced, it shows that the terrain is relatively flat. When the contours are close together, the landscape in that area is very steep. On most topo maps, every 5th line is a shade darker than the rest and has a number in the line to show the elevation.
- Longitude & Latitude
Overlying the entire map is a grid of straight lines. Each line is usually numbered on the map edge. These numbers are UTM’s (Universal Transverse Mercator) which can be used to pinpoint location. The grids – normally one km square on metric maps – can be used to estimate distance along your hiking route. As well, along the edges of the map, you will find numbers for latitude – degrees north or south of the equator – and longitude – degrees east or west of the prime meridian in Greenwich, England. If you’ve ever used GPS unit, you’ll be familiar with UTM’s and lat and long descriptions. The Brooks-Range All-In-One UTM reader comes in handy when working with maps.