All about map scale

A most important property of every map is its scale. Understanding map scales will help you decide what kind of map is best for your purposes and to evaluate alternatives.

Scale is the ratio between the length of a feature on the map and the actual length of the same feature on earth. As you shop The Map Center you will find that our product information often includes a ratio such as 1:30m or 1:500k. This ratio is the representative fraction, a brief, versatile way to state a map's scale. It works for people who think metric, miles, or whatever. This is simpler than you may think!

Say your house is 50 feet long and you draw a floor plan of it that is 1 foot long. Here are six ways to say the same thing.

1:50 is the representative fraction of that floor plan.
The drawing is one fiftieth of actual size.
One inch on the drawing represents 50 inches on the floor.
One millimeter on the drawing depicts 5 centimeters on the floor.
A room one pinkie finger long on the drawing is 50 pinkie fingers long in your house.

The representative fraction functions with any unit of linear measure as long as you use the same unit on both sides of the ratio. The number on the right side of the representative fraction is really the "bottom number" (the denominator) of a fraction just like the familiar 1/2, 1/8 or 1/50. The bigger the denominator, the smaller the fraction. We call 1:10,000 a large map scale and 1:1,000,000 a small scale because a millionth is smaller than a ten thousandth.

These abbreviations are used in the Map Center database.

k or K = thousand
m or M = million
var = variable. Usually means that the publication includes several maps at various scales.
na = not applicable or not available

Examples

33k = map scale 1:33,000
1.75M = map scale 1:1,750,000
50k/12.5k = main map scale is 1:50,000; major inset(s) 1:12,500; or 2 sided map.

The one perfect map would be a reasonable size, cover a very large area AND show every small detail. Well, no map can do all three. The tradeoff whereby depiction of physically small features decreases as area mapped increases is inescapable. This table shows a range of map scales with typical applications and characteristics of each.

Representative Fraction Appx. Miles per inch

Description

1:10,000  1/6 mi. Appropriate for a small city or the downtown of a large one, this scale permits all streets to be clearly shown and labeled, sometimes with one-way arrows. Pedestrian passageways, attractions, monuments and "Footprints" of buildings can be shown.
1:24,000 3/8 mi. Generally adequate to show and name all city streets. The popular USGS topographic maps at this scale can show bends in foot trails and practically every pond and watercourse.
1:50,000 4/5 mi. A city street map at this scale is crowded with small lettering and may omit some streets or names. Scale is ample to map connecting roads and major streets.
1:100,000 1 5/8 mi Fairly complete presentation of country roads, lakes, streams and parks is possible. An urban street grid may be depicted, but there is no room to label individual streets.
1:250,000 4 mi In rural areas, very minor dirt roads can be shown. Good for metro area maps that show roads "to and through" cities. Nearly all towns and villages can be identified.
1:500,000 8 mi Typical highway maps of small to medium sized states or small countries use a scale close to this. Small towns in crowded areas may be omitted.
1:1,000,000 16 mi Typical highway maps of large states or European countries use a scale like this.
1:5,000,000 79 mi A wall map of the United States may be at this scale.
1:10,000,000 to 50,000,000 158 - 789 mi These small scales are for maps of continents and the world.

For some wall maps our database provides miles per inch. Example: 8.5mi/in. You can translate any representative fraction to miles per inch if you remember that there are 63,360 inches in a mile.  For example, 1:250,000 means one inch on the map equals 250,000 inches on the ground.  250,000 divided by the number of inches in a mile, 63,360 equals 3.95.  Scale 1:250,000 is about 4 miles per inch.

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