Physical Geography 102
Maps and Location Systems
What is a map?
Graphic representation of a given area - a drawing
Can cover a large area
Can cover a small area
Can be detailed, generalized or cartooned
Language of Maps: Map Reading
Maps contain large amounts of information but unless you can read that information it won't do you any good
Problem: How do we represent the surface of a sphere on a map?
- direct representation - no distortion
- limited in size
- not easily transported or moved
2. Flat Sheets
Problem with a flat sheet is that it is not possible to flatten a sphere without distorting the surface
- Undevelopable geometric figure -cannot be flattened without distortion.
- Developable geometric figure- can be flattened without distortion: cylinder, cone, plane
Projection of the surface of a sphere onto a developable surface
- imagine a lightbulb at the center of the sphere and the lines on the sphere casting shadows on the surface of a developable figure
a. Plane in contact with one point of the sphere
b. Polar Projection is most common type
a. Cone apex is located directly above the pole
b. best for mid-latitude maps
a. Cylinder oriented parallel to axis
b. Mercator Projection is most well known
- developed by Gerhardus Mercator, Flemish cartographer. It has the property that any straight line drawn on the surface has a constant compass bearing - used in naval navigation
Interupted and Condensed Projections
a. broken surface
b. condensed - unneeded parts are omitted.
Map Location Systems
Global System - Longitude and Latitude
1. Longitude lines - "Meridians" - "Great Circles"
- north-south lines on the globe - all intersect at the North and South Poles
- measured in degrees East and West of the Prime Meridian
2. Latitude lines - "Parallels"
- East-West lines on the globe
- measured in degrees North and South of the Equator
Local Location System
1. Public Land Survey System
- Township and Range
Basic Map Information
All maps should contain the following information
Title - clearly and concisely describes the map location
Date - indicates the date of publication or revision
Location - Longitude and Latitude; Public Land Survey System; Inset Map.
Directional Orientation - Compass direction - if no compass direction is given, the standard convention is that north is at the top of the map
Legend - Information on the symbols used on the map
a. Ratio Scale -ex. 1:24,000 - 1 inch on the map = 24,000 inches on the ground
b. Bar Scale - allows direct measurement of the ground distances
Some of the Major Types of Maps
• Environmental - Landscape, Vegetation, Precipitation, Climatic, etc.
• Geographic Maps - Political, Country, State, Local, City, Highway, Road
• Statistical - Population, Economic
What is a topographic map?
The main purpose of a topographic map is to provide infromation on the elevation of the land.
Elevation and Relief Elevation is the altitude or height above mean sea level
Mean sea level = 0 ft or 0 m elevation
Relief is the vertical distance between to elevations
Contour Lines Elevations are represented on the map by contour lines
Contour lines are lines of equal elevation
Everywhere along a given contour line is at the same elevation
Basic Rules of Contour lines:
1. Relief between adjacent contour lines is constant - contour interval.
2. Contours crossing a stream form a "V"-pattern with the V pointing up hill.
3. Contour lines never cross or split.
4. The spacing of contour lines reflects the steepness of the slope - contour lines far apart = gentle slope - contour lines close together = steep slope
5. Hills and knobs are shown by closed contours.
6. Closed depressions are indicated with hatchures pointing down hill.
7. The shape of the contour reflects the shape of the ground.