All you need to know about Map Scales from The Map Shop

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Although we may not realize it, we all consider the scale of a map every time we look at one. Without some mental picture of scale, looking at a map to consider a route plan, a sales territory or a vacation is completely meaningless. The worst possible scenario is to make some decisions about one of the endeavors above with a misconception of scale. How many times have you heard someone say, "Gee, it looked closer on the map".

All good maps have their scale represented on the mounting rails Most use a scale bar like the one shown below. Others will tell you that one inch or one centimeter on the map equals a certain number of miles or kilometers on the ground. Some maps will show both; although there is a reason why some mapmakers are reluctant to express the scale of their map in terms or inches or centimeters. We will get into that later.

Here is a typical scale bar in miles
Here is the same scale bar in kilometers       By having a ruler-like appearance, the scale bar makes it easy for someone to judge distance. Notice that the scale bar for 4 kilometers is shorter than the scale bar for 4 miles. Thatís because a kilometer is shorter than a mile and therefore the same distance on a map will be a greater number of kilometers.

Yet another way to express scale is with a ratio. The scale bars above show that approximately one inch on the map equals one mile on the ground. That map would have a ratio scale of 1:63360. What the mapmaker is really telling you is, 1 inch on the map equals 63360 inches on the ground. In other words, one mile is 5280 feet times 12 inches to the foot which equals 63360. What if the map had a scale expressed as one inch equals 3 miles. Then the ratio form of the scale would be 1:190080. (63360 times 3)

The beauty of scale expressed as a ratio, is that it does not matter if you measure the map in metric or English units. It simply expresses a ratio between the size or distance between features on the map versus the same distance in the real world. If the map scale is 1:63360 that is also saying that the actual distance between two points on the map is 63360 times larger than is shown on the map.

Some of our customers ask for larger maps, assuming that as maps get larger, the amount of detail will increase. This assumption is not necessarily the case. In our digital age, it is often easy to print a map at a larger size. This automatically increases the size of the features on the map, but the cartographer does not necessarily add more detail to take advantage of the additional space on the map. This is one reason why map-makers like the scale bar only method of showing map scale. The scale bar automatically and proportionally increases in size as the map is enlarged. Thus its representation of scale does not change as the map size is increased.

Here are some typical scales found on various types of maps.

Map type 1 inch equals Scale
City street atlas (Our Professional Driverís Atlas) About a quarter mile 1:18,500
USGS topographic map About 3/8thís of a mile 1:24,000
City / county folding map About ĺís of a mile 1:40,000
State travel map 14 miles 1:880,000
US map 50 miles 1:3,000,000
World map 300 miles 1:20,000,000

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