How to Use and Understand Maps: Definitions

A map is an abstract representation of the physical features of a portion of the Earth's (or some other planet's) surface graphically displayed on a planar surface (generally, a sheet of paper). Maps display signs, symbols, and spatial relationships among the features. They typically emphasize some features, generalize others, and omit certain features from the display to meet design objectives. (Adapted from Pennsylvania Spatial Data Access (PASDA)'s ArcView Tutorial glossary.)

Scale is defined as the ratio of the distance on the map to the distance on the ground.

• 1:1 is the real world: 1 unit on the map = 1 unit on the ground.
• A scale of 1:63,360 means that 1 unit on the map = 63,360 units on the ground.
• If that unit is 1 inch, 1 inch on the map = 1 mile (63,360 inches) on the ground.

What is considered large scale and what is considered small scale?

• A map of the world on an 8-1/2 x 11 sheet of paper might have a scale of 1:30,000,000. A 30-inch by 30-inch map on one sheet of the City of Seattle topographic map set has a scale of 1:2,400.
• 1:30,000,000 is a smaller scale than 1:2,400. Think of it like fractions: 1/30,000,000 is smaller than 1/2,400. Therefore 1:30,000,000 shows less detail than 1:2,400.
• A small scale map shows less detail for a large area. The world map, with a scale of 1:30,000,000, shows many countries with little detail.
• A large scale map shows more detail for a small area. City of Seattle topographic maps at 1:2,400 show details within neighborhoods, but each sheet does not cover very much territory.

For more information on map scales, see the USGS factsheet on Map Scales.

The latitude of a point is defined as the elevation angle of that point above or below the equator.

On the globe, lines of constant longitude ("meridians") extend from pole to pole, like the segment boundaries on a peeled orange. The longitude of a point is defined as the marked value of that division where its meridian meets the equator.

NASA provides an explanation of latitude and longitude with diagrams.

In 1785 the Continental Congress adopted legislation that laid down the system for surveying the lands of the West. A public land survey divided and subdivided the United States into squares that could then be mapped and sold. This grid system covers the entire United States, except for the original 13 states, and is still used today to specify locations. This system is commonly called Township and Range.

• Base Line: The horizontal line where the survey began.
• Meridian: The vertical line where the survey began. Washington and Oregon are on the Willamette Meridian.
• Section: A square mile numbered between 1 and 36 containing 640 acres.
• Township: A six by six mile square containing 23,040 acres divided into 36 sections. Also used for the measure of township squares north or south of the base line.
• Range: The measure of township squares east or west of the meridian.

Please consult the following resources for more details:

• The UW Map Collections' guide to Township and Range: An Explanation for Washington State.
• About.com's guide to Township and Range: The United States Public Lands Survey.
• The Bureau of Land Management's Map of Principal Meridians and Base Lines for the United States Public Land Surveys.