Earth Science – Unit 1.1
Reading Topographic Maps
Topographic Maps Outline
- 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
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
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
Projections: Equal Distance vs. Area
Equal Area Cylindrical
Equidistant Cylindrical
Orthographic Projection: Orbital View
Othographical
UTM – Universal Transverse Mercator
•
•
•
•
Cylindrical (transverse)
Conformal
Scale is true along Central Meridian
Used extensively for quadrangle maps
at scales of 24,000 from 250,000
• 60 zones, 6 degrees each.
UTM Zones of the Lower 48
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.
1
0
1
2
3
4 Miles
Example:
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
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
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.
- 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
Topographic Profile
Constructing a Topographic Profile