by Jim Riesterer . . . . . . . . . . Edited by Scott Hughes, Dan Narsavage & Diana Boyack
Topographic Maps Tutorial
Introduction & Materials
What is a Map?
Using Topo Maps
Map Scale
Reference Datum
Map Projections
Distortions
Grid Systems
Geographic
UTM
State Plane
Public Land Survey
Vertical Scale
Creating Profiles
Vertical Exaggeration
Calculating Slope
Using a Compass
Magnetic Declination
Get a Bearing
Go from A to B
Find Self on a Map
Topographic Maps Field Exercises
Exercise 1
Exercise 2
Exercise 3
Exercise 4
GeoSTAC Home
Field Exercises
geostac@gmail.com
April 8, 2008
Finding Self on a Map
Now you know how to get from point A to point B on a map using your compass…but what if you are not sure where exactly point A is (i.e. you are lost)? By far the easiest way to determine where you are on a map is to pull out your pocket GPS (global positioning system receiver) and have it give you your map coordinates. If, however, you are like a lot of people, you don’t want to shell out a few hundred bucks for a GPS and, unless you are in an area with very little topographic relief, you don’t need one. You can determine your position quite accurately on a topographic map by using your compass to triangulate between three points.
The first step in triangulation is to pick three topographic features that you can see and can identify on your map (mountains are ideal). Start with the first feature you have chosen and determine the bearing between you and it, as outlined above. Once you have determined its bearing, pencil in a line with the same bearing on your map that runs through the chosen feature (once again, having a protractor would be useful).
Repeat this for the other two features, drawing lines for each. The point where the three lines intersect on the map is where you are. Depending on how accurate your sightings were and how accurately you drew your lines through the features, there will probably be a some error in your location. Be sure to double check the map and reconcile it with what you see. If the lines intersect in a valley and you are on a hill, the location is obviously off a bit on the map.
It does give a good approximation though and, by looking at your surroundings, you should be able to figure out which hill on which side of the valley you are on. If you have an altimeter with you, you can also use it with the triangulation to help determine your exact location more accurately.