Cartography Basics:How Geographic Data are Stored and Represented

Maps

Images: air photos, satellite images

Databasesorganized sets of data that are required for a specific purpose

Some categories of maps (as well as images and databases):

Small-scale vs. large-scale

Reference vs. thematic

Scale

Ratio between the size of the earth’s features on the map and the size of the same features on the ground.

Verbal scale: “1 inch equals 5 miles” Bar scale

3 Ways of indicating scale ..

0 10 20 30km

• Representative fraction: “1:24,000”

What unit of distance is used in this scale?

The numerator is always 1

1:10,000 means:• one inch on the map equals 10,000 inches on the earth• one cm on the map equals 10,000 cm on the earth

What is an advantage of using RF to indicate scale?

Representative fraction (RF):

124,000

1:24000 =

Large-scale vs. small-scale: Small scale: the map is small compared to the

reality

Large scale: the map is large (relatively) compared to the reality

LARGE scale is when the RF is large (that is, the denominator is small)

SMALL scale is when the RF is small

Large scale vs. small scale

1:24,000 1:100,000

124,000

1100,00

0

Summary: Large vs small scale

Large scale Small scale

Map is large compared to reality

Map is small compared to reality

RF is a larger number:

1:24,000

RF is a smaller number:

1:250,000

Which is the larger-scale image?

Which is the larger-scale RF?

1:50,000 1:200,000

Reference mapsvs.

Thematic maps:

Reference maps:• Emphasize spatial location

Thematic maps:• Emphasize spatial patterns

Planimetric maps

Any map that doesn’t attempt to show “relief features” of earth

Cadastral map

Topographic

Greek: Topos=place + graphien=to describe Maps that do show the shape of the terrain

Bathymetric maps

Show water depth Bathymetric map of 1855

Reference or thematic?

Reference or thematic?

Reference or thematic?

Reference or thematic?

Reference or thematic?

Reference or thematic ?

“Cartogram”

What common element of most maps is missing from a cartogram?

Leading candidate, by county

Summary:Ways of representing geographic

information

Maps

Images

Databases

•Small-scale vs. large-scale

•Reference vs. thematic

Mapping the “where”