compass use & land measuring. terms to know: magnetic declination: the angular variation of...
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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