Compass Use & Land Measuring

Terms to know:

MAGNETIC DECLINATION: the angular variation of magnetic north from true north; declination may be either east or west

AGRONIC LINE: the line of zero declination (no correction needed)

ISOGONS: lines having equal declination

BEARINGS: horizontal angles that are referenced to one of the quadrants of the compass (NE, SE, SW, NW)

AZIMUTHS: comparable angles measured clockwise from due north, thus reading 0o to 360o

SURVEYING: the art of making field measurements that are used to determine the lengths and directions of lines on the earth’s surface

PLANE SURVEYING: the measurement of distances & angles, the location of boundaries and the estimation of area; this is what a forester is concerned with

Measurement lengths to know:

One chain = 66 feet

One chain = 100 links

One link = 7.92 inches

One acre = 10 square chains

One acre = 43, 560 square feet

One mile = 5,280 feet

How to use the compass

Make sure:• The compass is perfectly level• The sights are properly aligned• The needle swings freely• All readings are taken from the

North End of the needle.

Area formulas to know

Area of a squareFormula: (S)2

Area of a rectangleFormula: L x W

Area of a triangleFormula: 1/2BH

The main formula that we will use is Hero’s formula. This is used to

calculate the area of a triangle when you know the three sides.

Formula: Area=square root of s(s-a)(s-b)(s-c)s= a + b + c

2

Legal Land Descriptions

History:Ordinance of 1785 established the rectangular surveying system as developed by Thomas Jefferson

13 original colonies, Ohio, Tennessee & Kentucky were surveyed with metes & bounds

Metes & bounds system was not accurate since it followed natural land features such as ridges, streams, etc.

States west of Ohio were surveyed using the rectangular surveying system

Rectangular surveying system

Subdivided land into square areas by using Principal meridians and base lines

Meridians run north & south

Base lines run east & west

Ranges

A six mile strip of land which runs north & south parallel to the principal meridian

Labeled with consecutive numbers east or west of the principal meridian

Townships (also called tiers)

A six mile strip of land that runs east & west, parallel to the base line

Labeled with consecutive numbers using the south baseline as the starting point

Subdivided into a rectangular grid of 36 sections. Each section is one square mile.

Contains 36 square miles and is six miles square

Each section is divided into quarters for reference purposes

Quarter sections are 160 acres each & are abbreviated as SE ¼, SW ¼, NE ¼, or NW ¼

Quarter sections can be divided into quarters or halves which can be further divided into quarters.

Description of land within a section must be read backwards

Legal land descriptions for every piece of property can be found in the county plat books.

One township is displayed per page with all the land tracts separated by property owner/s

Each land tract list owners & acreage

Smaller acreages, especially subdivision lots, are not individually shown

Plat books are not accurate enough to locate exact property boundaries