How To Use and Understand Maps
What Is a Map?
What Is Scale?
What Are Latitude and Longitude?
What Are Township and Range? (Public Land Survey System)
How Do I Browse for Maps for a Specific Country or Geographical Region?
How Do I Interpret Library of Congress Map Call Numbers?
How Do I Interpret Topographic Map Symbols?
Map Skills Bibliography and Other Cartographic Reference Tools
What Is A Map?
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.)
What Is Scale?
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.
What Are Latitude and Longitude?
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.
What Are Township and Range? (Public Land Survey System)
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:
How Do I Browse for Maps for a Specific Country or Geographical Region?
Consult our LC Map Call Numbers Finding Aid, an alphabetical list of countries,
regions, states, and cities with an emphasis on the Pacific Northwest.
How Do I Interpret Library of Congress Map Call Numbers?
Library of Congress call numbers for maps can be broken down into several
basic components:
|
- where,
- what,
- when,
- which scale, and
- who.
|
(As you can see, not every component is present in every call number.)
Where is represented by the letter G and four numbers. Consult
our partial list of geographic areas for
more information.
What—that is, the subject matter of the map—is a bit more
complicated.
Each geographic area can be additionally broken down by subdivisions,
based on the last digit:
- 0 or 5—a general map of the geographic area
- 1 or 6—map of a subject within that area (roads, geology, etc.)
- 2 or 7—map of a region or natural feature (body of water, mountains,
island, etc.)
- 3 or 8—map of a major political division (county, state, province,
etc.)
- 4 or 9—map of a city or town
So, for example, if G4280 is the general call number for Washington
State,
- G4281 indicates that the map is about a subject within the state
of Washington (ex. mineral resources)
- G4282 indicates that the map is about a region or natural feature
within Washington (ex. Mount Rainier)
- G4283 indicates that the map is about a major political division
(ex. King County)
- G4284 indicates that the map is about a city or town (ex. Issaquah)
A general map (ending in 0 or 5) will not have a subdivision. All other
kinds of maps (ending in 1-4 or 6-9) will.
When—the date of publication—is represented by a
year. If the year of publication is not known, it will have a question
mark and may also have one or more dashes. For example, 197-? indicates
that the cataloger believes that the map was published sometime in the
1970s.
Which scale is only used for sets of maps all in the same
scale, such as topographic sets. It is represented by the letter s and
a number. For example, s250 represents the scale of 1:250,000.
Who—the author of the map—is represented by a period,
one letter, and one or more numbers. This is called a Cutter number
or a Cutter.
Examples:
- A general map of WA state has the following call number:
G4280 1987 .A4
where (G4280—WA state), when (1987), who (.A4—Allen Cartography)
- A map of the roads of Seattle has the following call number:
G4284.S4P2 1999 .T5
where (G4284—WA state by city; .S4—Seattle), what (P2—roads),
when (1999), who (.T5—Thomas Bros. Maps)
- A topographic map of India has the following call number:
G7650 s250 .I5
where (G7650—India), which scale (s250—1:250,000), who (.I5—the
Indian government)
How Do I Interpret Topographic Map Symbols?
The United States Geological Survey (USGS) has a detailed description
of topographic map symbols.
Map Skills Bibliography and Other Cartographic Reference Tools
Last modified: Monday March 03, 2008
Questions? Comments? Please email us at maplib@u.washington.edu
