Understanding a Topo map (before you head out!)
HIKING BACKPACKING CAMPING CANOEING, whatever your choice for an outdoor recreational activity, a topographic map is a must-have in an outdoor adventurer’s toolkit. Topographic maps accurately represent, to scale, the earth’s features on a two dimensional surface. Every feature shown on topographic maps is where it actually is on the earth’s surface.
A map represents a given area on the ground, and its scale is determined by the amount of real-world area covered on the map. Map scales refer to the relationship (or ratio) between the distance on a map and the corresponding distance on the ground, and can also be shown using a scale bar (usually found at the bottom of the map).
Different scales are used in different countries. For instance, in the US, the United States Geological Survey (USGS) publishes maps with 1:250,000, 1:100,000, 1:62,500 and 1:24,000 map scales, and in Canada, there are two map scales, 1:250,000 and 1:50,000. The first number of the scale resents a core unit of distance on the map, while the second represents that same distance on the ground. So, for a 1:24,000 map sheet, 1 inch measured on the map is equivalent to 24,000 inches in the real world. There are over 54,000 map sheets that cover every inch of the United States.
Maps are also known as large scale and small scale. Large scale includes map scales ranging from 1:2,500 to 1:50,000 while small scale includes map scales 1:250,000 to 1:7,500,000. A large scale provides more detail, but covers less ground area on the map and a small scale provides less detail, but covers a larger ground area on the map. Remember, the smaller the ratio, the larger the scale.
Different map scales provide different levels of details in terms of features presented. The map scale used for most US topographic mapping, and the most detailed, is the 1:24,000 or the 7.5-minute series. Maps at this scale cover an area measuring 7.5 minutes of latitude and 7.5 minutes of longitude and are commonly called 7.5-minute quadrangle maps. There are four 7.5 minute quads per fifteen minute quad, 32 per one degree sheet, and 128 per two degree sheet. One map covers approximately nine miles in a north-south direction and approximately 6.5 miles east-west and is approximately 29 inches high and 22 inches wide.
Maps at this scale are useful because topographic features are easy to identify, which allows for accurately determining your location. Also, the clarity of topographic features makes route-finding easier. They provide detailed information about the features of an area, including the locations of important buildings and most campgrounds, water mills, footbridges, fence lines, and private roads. They also provide excellent detail, including mountains, valleys, plains, lakes, rivers, streams, woods, vegetation, elevation contours, and railroads.
Also suitable for recreational and other activities is the 1:62,500. It provides enough detail to determine location with good accuracy. These maps cover about four times the area of one 7.5-minute map.
Other map scales in common use for topographic maps are 1:100,000 (one degree sheet) and 1: 250,000 (two degree sheet). These map scales are best for giving an overview and are useful for hunting and other activities where coverage of a large area is more important than detail. They show large areas on single map sheets, but details are limited to major features, such as boundaries, parks, airports, major roads, railroads, and streams.
Map scales control not only how features are shown, but what features are shown, and that’s why when you are planning a trip, the most important consideration in choosing the right map scale is its intended use.
To plan your hiking, backpacking or camping trip, choose the appropriate maps for your intended destination. The 1:24,000 or 7.5 minute map series are the maps of choice for hiking, backpacking, canoeing, camping and fishing. The main drawback of this map series is that several maps may be needed to provide coverage for a large area. Map scales of 1:100,000 and 1:250,000 aren’t recommended for back-country use because of the lack of topographic detail.
Before setting out, study the map and find your start and finish points. The terrain depicted on the map will help you select a suitable route, and anticipate and make best use of the features you’ll encounter. With a topographic map in front of you, you can estimate the length of your proposed adventure.