Introduction to Topographic Maps Banner link to home page GeoSTAC Link to Department of Geosciences at Idaho State University
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
Grid Systems
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
April 7, 2008

Public Land Survey System

The final grid system discussed here is the public land survey system (PLSS). Although the geographic, UTM, state plane, and PLSS coordinate systems are the most common, there are other coordinate systems in use today. The public land survey system is most often used on topographic maps published in the United States and has its roots in the early surveys of North America in the 1700's.

public land survey image

The PLSS system differs from the coordinate systems described above in that it is more descriptive, and relies less on absolute measurements of location. It is a good way to give a quick approximation of a location, but the main drawback is its lack of accuracy.

In each state (except for the original thirteen states and a few in the southwest that were originally surveyed based on Spanish land grant boundaries), early surveyors established a principal meridian running north-south, and a base line running east-west.

These initial survey lines served as a basis for subsequent survey lines spaced at 24 mile intervals along the eastern, western, and southern boundaries. (Why not the northern boundary as well? ? ? . . . Think of the relationship between latitude and longitude).

Further subdivision of these ‘squares’ led to the creation of 16 smaller squares measuring six miles on a side (see diagram). When measuring in a north-south direction, each of these squares is called a township (in some localities a township is referred to as a tier).

When measuring in an east-west direction, each of these squares is called a range. So, a 36 square mile area located between six and twelve miles east of the principal meridian and twelve to eighteen miles north of the base line would be called township three north, range two east (written as T3N., R2E). Each township (or tier) is further subdivided into 36 smaller squares covering roughly 1 square mile.

These areas are called sections and are numbered within a township from the upper right to the lower right in an alternating manner (1 to 6 are numbered from right to left, 7 to 12 from left to right, etc.). These one mile squares are the smallest formal subdivisions in the PLSS system.

But to describe a location the squares are quartered, and then the quarters are quartered again, as shown. The location of the star in the figure above would be described as the southeast quarter of the southeast quarter of the northeast quarter, section thirteen, township two south, range two west. The shorthand for this is: SE1/4, SE1/4, NE1/4, sec. 13, T2S., R2W.

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