In 30 states, mostly west of the Appalachians, USGS topo maps carry a red grid. That's the Public Land Survey System (PLSS). Land is divided into townships about 6 miles square, and each township is split into 36 sections of about one square mile. Legal land descriptions, property lines, and many hunting and access rules are written in these terms, so it pays to know how to read them.
What are the red lines on a topo map?
Red lines on USGS topo maps are usually Public Land Survey System lines: township and range lines about every 6 miles and section lines about every mile. Red numbers from 1 to 36 are section numbers, and labels like T2N and R3W name the township and range.
IN THIS GUIDE
Townships and ranges · Sections · Survey corners · Other land surveys · Using the section grid · FAQ
Townships and ranges
Townships are counted north or south of a baseline, and ranges east or west of a principal meridian. Line style tells you how reliable the position is.
Range or Township line
A solid red line: a township or range line that was surveyed and is accurately located.
Range or Township line – location approximate
Long red dashes: the line was surveyed, but its exact position on the map is approximate.
Range or Township line – location doubtful
Widely spaced red dashes: the position is doubtful.
Range or Township line – protracted
Short red dashes: a protracted line, projected onto the map from survey plans but never surveyed on the ground. Common in rugged or remote country.
Range or Township line – protracted (AK 1:63,360-scale)
A gray line: protracted township lines on Alaska's 1:63,360-scale maps.
Range or Township labels
Red labels in the margin and along the lines. R1E is Range 1 East and T2N is Township 2 North. Gray labels are for protracted townships.
Sections
Each township holds 36 sections, about 640 acres each, numbered back and forth starting from the northeast corner.
Section line
A thinner red line, about every mile: a surveyed section line.
Section line – location approximate
Long red dashes: a section line whose position is approximate.
Section line – location doubtful
Widely spaced red dashes: position doubtful.
Section line – protracted
Short red dashes: a protracted section line that was never surveyed on the ground.
Section line – protracted (AK 1:63,360-scale)
A gray line: protracted section lines on Alaska's 1:63,360-scale maps.
Section line – section numbers
Red numbers from 1 to 36 in the middle of each section. Section 1 is in the northeast corner of the township, the numbers snake back and forth, and 36 is in the southeast corner. Gray numbers are for protracted sections.
Survey corners
Corners are where the survey was physically marked on the ground with stones, posts, pipes, or brass caps. A found corner means the original marker was located.
Found section corner
A bold red cross where section lines meet: the original section corner monument was found.
Found closing corner
A red T-shape: a closing corner, where a survey line ends against another survey or boundary that was already in place.
Witness corner
A red cross labeled WC. When the true corner falls somewhere a marker can't be set, such as in a stream or on a cliff, surveyors set a witness corner nearby.
Meander corner
A red mark labeled MC, where a section line meets the bank of a lake or large river. Surveyors "meandered" along the shore between these points.
Weak corner USGS–Forest Service quads
A thin red cross: a corner whose location is less certain.
Other land surveys
Not all land was laid out by the PLSS. Older grants, claims, and state surveys get their own symbols.
Range or Township line
A red dotted line: township lines from surveys other than the federal PLSS.
Section line
A finer red dotted line: section lines from other surveys.
Land grant, mining claim, donation land claim, or tract
A red line with dot pairs: boundaries of Spanish and Mexican land grants, patented mining claims, Oregon donation land claims, and similar tracts.
Land grant, homestead, mineral, or other special survey monument
A small red square with a center dot: a monument from a land grant, homestead, mineral, or other special survey.
Fence or field lines
Fine dashed lines: fences or field lines that mark property boundaries on the ground.
LEARN TO READ A TOPO MAP
Topo Map Reading Intro: Learn how to read topographic maps in 10 sessions
A one-minute lesson from our Topo Map Reading series.
Watch the full Topo Map Reading series →Using the section grid
- Read a legal description from small to large. "NE¼ of Sec. 12, T2N, R3W" means the northeast quarter of section 12, in Township 2 North, Range 3 West.
- Use sections as a built-in grid. Each square is about a mile on a side, so you can estimate distances at a glance.
- Don't treat map lines as legal property lines. Section lines show the survey, not who owns the land. Check with the county or the land management agency before you cross a boundary.
- Watch for irregular sections. Sections along the north and west edges of a township, and near rivers and old grants, are often oddly shaped where the survey was corrected.
PUT IT TO USE
See these symbols on a real map
Frequently asked questions
How big is a section on a topo map?
A standard section is about one mile on a side, or 640 acres. A township holds 36 sections and is about 6 miles on a side.
How do you read T2N R3W?
T2N means the second township north of the survey's baseline. R3W means the third range west of its principal meridian. Together they identify one township.
Why don't all states have township and range lines?
The original colonies, Texas, and a few other states were surveyed before or outside the federal Public Land Survey System, so their maps use other survey systems or none at all.
What does WC mean on a topo map?
WC stands for witness corner: a marker set near a survey corner when the true corner falls somewhere a marker can't be placed.
MORE SYMBOL GUIDES
Boundary Lines on Topo Maps: States, Counties, Parks & Public Land · Benchmarks & Spot Elevations: What BM Means on a Topo Map · Map Grids on Topo Maps: Latitude, Longitude, UTM & State Plane
← Back to all USGS map symbols
Symbol artwork from the U.S. Geological Survey Topographic Map Symbols brochure (public domain).