FIELD METHODS IN
ENVIRONMENTAL
GEOLOGY LABORATORY
GEOS 3110
Topographic Maps
- Definition
- Features
- Elements
- Contour lines
- Cross-section representation
- Exercise
Definition of Topographic Maps
1. A graphical representation of the three dimensional shape
of the earth’s surface.
2. A reduced, simplified, categorized/classified, symbolized and
annotated representation of the earth’s surface which has been
projected on a horizontal plane.
Features of Topographic Maps
TOPOGRAPHY (RELIEF):
- printed in brown
- contour lines shows hills, mountains, plains, etc.
WATER FEATURES:
- printed in blue
- includes oceans, lakes, ponds, rivers, canals, etc.
CULTURE:
- printed in black
- human-make works such as roads,
railroads, buildings, land boundaries, etc.
Features of Topographic Maps
Relationship between 3D and 2D representation
3D view
2D view
(after Zumgerbe, Rutford, Carter, 1996)
Title and Location
MAP TITLE
Title and Location
QUADRANGLE LOCATION
Map design
Other Information
Earth's Surface Location Coordinates
Position on the surface of a sphere is most easily described by
angle from the pole (N-S position), and from some defined
'prime meridian' (E-W position). These are usually given as:
- parallels - latitude (angle from equator)
- meridians -longitude (angle from Greenwich, England)
So:
Latitudes are a family of lines drawn on the globe parallel to
the equator.
Longitudes are circles drawn on the globe that pass through the
two poles.
Latitude and Longitude
Generalized system of meridians and parallels
(after Zumgerbe, Rutford, Carter, 1996)
Projection
DEFINITION
The process of constructing a map, the transferring of the
meridians and parallels to a flat sheet of paper.
The resulting product of this geometric exercise is called
a 'map projection'.
This can be done in a wide variety of ways, the principle differences
being projections that show accurate area over the entire map,
and those that show accurate distance.
Type of Projections
Transformation from lat/long to a flat surface
(after Geological Survey Bulletin 1532, 1983)
Projections: Equal Distance vs. Area
Equal Area Cylindrical
Equidistant Cylindrical
Orthographic Projection: Orbital View
Othographical
Map Scale
Definition
A means of showing the relationship between the size of an
object or feature indicated on a map and the actual size of the
object on the ground.
Scale is expressed as a ratio, such as 1:24,000 (i.e. 1 unit on the map
equal 24,000 units on the ground) and shown graphically by
Scale bars marked in feet and miles or meters and kilometers.
Scale Types
Fractional scale: - is a fixed ratio between linear measurements on
the map and corresponding distances on the
ground. It is sometimes called the representative
fraction or R.F.
Example: R.F. 1:62,500
Graphical scale: - is simply a line or bar drawn on the map and
divided into units that represent ground distances.
Example:
1
0
1
2
3
4 Miles
Verbal scale: - is a convenient way of stating the relationship of map
distance to ground distance.
Example: 1 inch equals 1 mile
Scale
Decreasing Detail
Increasing Coverage
1:24,000 scale
1:100,000 scale
1:125,000 scale
(after Zumgerbe, Rutford, Carter, 1996)
Declination
True North
(Through the Poles)
Magnetic North
Legend
Contour lines
DEFINITION
A contour line is an imaginary line on the surface of the
earth connecting points of equal elevation.
Topography is the configuration of the land surface and
is shown by means of contour lines.
The contour interval (C.I.) is the difference in elevation
between any two adjacent contour lines.
Contour lines
Relationship between topographic features and contour lines
(after Hamblin, Howard, 1975)
General Features of Contour Lines
- contour lines connect points of equal elevation
- steep slopes are shown by closely spaced contour lines
- gentle slopes are shown by widely spaced contour lines
-contour lines do not intersect, branch or cross, except in a vertical
or overhanging cliff.
- contour lines can close on a particular map or on adjacent sheets.
- when contour lines cross streams they bend upstream; that is, the
contour line forms a 'V' with the apex at the intersection with the
stream, and pointing in an upstream direction.
- closed contours appearing on the map as ellipses or circles
represent hills or knobs.
- closed contours with hatchures, short lines pointing toward the
center of the closure represent closed depressions.
Topographic Profiles
DEFINITION
- A topographic profile is a diagram that shows the change
in elevation of the land surface along any given line.
- It graphically represents the 'skyline' as viewed from a
distance.
Topographic Profile
(after Zumgerbe, Rutford, Carter, 1996)
Topographic Profile
Constructing a Topographic Profile
(after Hamblin, Howard, 1975)