Introduction to Topographic Maps Banner GeoSTAC Home Page Department of Geosciences ISU
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

State Plane Coordinate System

The State Plane Coordinate System (SPCS) was developed in the 1930s by the U.S. Coast and Geodetic Survey to provide a common reference system for surveyors and mappers. The goal was to design a conformal mapping system for the country with a maximum scale distortion of one part in 10,000, which at the time was considered the limit of surveying accuracy. The State Plane Coordinate System (SPCS) is used for local surveying and engineering applications, but isn't used if crossing state lines.

The State Plane grid system is very similar to that used with the UTM system, with the exception of where the origin for the grids are located. The easting origin for each zone is always placed an arbitrary number of feet west of the western boundary of the zone, eliminating the need for negative easting values.  The northing origin, however, is not at the equator as in UTM, but rather it is placed at an arbitrary number of feet south of the state border.

To maintain the accuracy of one part in 10,000 and minimize distortion, large states were divided into zones, and depending on their orientation different projections were chosen. The three conformal projections used are listed below.

  • Lambert Conformal Conic... for states that are longer east–west, such as Tennessee and Kentucky.
  • Transverse Mercator projection... for states that are longer north–south, such as Illinois and Vermont.
  • The Oblique Mercator projection... for the panhandle of Alaska, because it lays at an angle.
U.S. State Plane System

The number of zones in a state is usually determined by the area the state covers and ranges from one to as many as ten in Alaska. Each zone has a unique central meridian.

Idaho uses a transverse Mercator projection and is divided into three zones - east, central and west.

  • Idaho East Zone: 1101 ... includes these counties: Bannock, Bear Lake, Bingham, Bonneville, Caribou, Clark, Franklin, Fremont, Jefferson, Madison, Oneida, Power, Teton.
  • Idaho Central Zone: 1102 ... includes these counties: Blaine, Butte, Camas, Cassia, Custer, Gooding, Jerome, Lemhi, Lincoln, Minidoka, Twin Falls.
  • Idaho West Zone: 1103 ... includes these counties: Ada, Adams, Benewah, Boise, Bonner, Boundary, Canyon, Clearwater, Elmore, Gem, Idaho, Kootenai, Latah, Lewis, Nez Perce, Owyhee, Payette, Shoshone, Valley, Washington.

For more information about each state's zones visit the following site:

The State Plane system orginally used feet as its primary unit of measure and was based on the North American Datum of 1927 (NAD27). Because of technological advancements in measuring the earth's size and shape some of the State Plane systems for states are being converted to North American Datum of 1983 (NAD83), and will use meters as the primary unit of measure.

With these changes some of the states are redefining zones and primary coordinates. For instance California changed from 7 zones to 6, Montana changed from 3 zones to 1, Nebraska changed from 2 zones to 1.

----- Useful links for more information -----

The following is an excellent site that explains state plane with an interactive map for each state.
Utilities for converting between Geodetic Positions and State Plane Coordinates or for finding an SPC Zone...

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