The direction of any lot line is measured in relation to a north-south line. This relationship or direction is commonly called hearing. The bearing of a line is the horizontal angle between the line and a line pointing true north-south. The bearing is identified by the compass quadrant and degrees. The quadrant refers to the general compass direction, such as NE, SE, SW, or NW and limited to 90°. Fig. 4-8 shows the quadrants labeled according to compass direction.
For example, line AB has a bearing of N50°E. This means that line AB is measured from north in an easterly direction of 50°. Line CD in this figure has a EF has a bearing of S 26° E. It is measured from south in an easterly direction, 26° from the north-south line. Bearings of lines used for surveying, site planning or land development purposes are always measured from either north or south and never greater than 90°.
Lot line bearings are related to true geographic north. A compass needle will point to the true magnetic north pole. Magnetic north and geographic north are not the same. The difference between the two norths is called the magnetic declination. The magnetic declination is found on all U.S. Government maps and charts. Remember true geographic north is always used in site planning! The bearing of N 79° W. Line CD is measured from north in a westerly direction. Both of these lines, AB and CD, have been measured from north. On the other hand, line shows a line; however, line GF is different fromFG even though it appears the same.
When referring to a line, some identification must be made. Letters are sometimes placed at the ends of a line. When discussing line GH, the first letter G means that this is the point or origin. The line begins at G and ends at H. When referring to line GH, it would have a bearing of 65° W. Using the same line, but identifying it as “line HG,” H would be the point of origin. The line begins at H and terminates at G and has a bearing of N 65° E. The first letter always indicates the point of beginning.
Length of Lines
Straight Lines. Any straight line in a site, plot, or land development plan is identified by its bearing and length. The length of the line normally is carried to the hundredths of a foot (.xx'), such as 135.60' or 78.69'. The bearing of the line may be placed before or after the length of the line, as N 02°-30' E 156.50' or 156.50' N 02°-30' E. If space is limited on a drawing, the bearing may be placed on one side of the line and its length on the other.
Dimension lines are normally not used to give the length and bearing of a lot line. Length of lot lines, distances of setback, side setback, etc. are always given in feet and decimals of a foot. These measurements are usually not given in feet and inches. All measurements regarding the site are given in feet and decimals of a foot (xxx.xx'). Features such as driveway and sidewalk width, length and depth of house, out buildings, pool, or any other items directly related to the house are generally given in feet and inches, (xx'-x”).
Curved Lines. Lines which are curved on the plot or development plan are also measured. As with the straight line, the length of the curved line is given along the line in feet and hundredths of a foot (xxx.xx'). The length of a curved line the bearing cannot be given for a curved line.For every curve that appears on the site plan, certain necessary information must be supplied. Curves which appear on plot or site plans are called horizontal circular curves. The designer, as well as the contractor, must have some information about the curve(s) forming part of the lot line. The same curve that appeared in the preceding figure, but with some explanatory information. When describing a curve some basic terms must be understood. Some of these are:
- PC denotes Point of Curvature. PC is called out where the curve begins. It is at this point where the curve is tangent to line AX.
- PT means Point of Tangency. This is the terminal point of the curve and indicates where it is tangent to line XB.
- T indicates Tangent lines. These are identified by the two straight lines marked T. The tangent lines join the curve. The curve is tangent to AX and XB and lines PCO and PTO are at right angles to AX and XB. The intersection of lines from the PC and PT form the center point of the arc.
The angle formed by lines PCO and PTO is called the central angle or interior angle. Information about any curve is given in tabular form. Each curve is identified by a number or letter placed in a balloon or cherry. All necessary information about the curve is given in the table. Giving curve data in tabular form rather than placing it on the curve is the easiest and accepted standard. If each dimension for the tangent distance.
Depending upon the original survey, all of the information (radius, central angle, tangent, chord, chord bearing, and arc) may not necessarily be given. Three of the 6 pieces of data must be identified. These are: (1) Radius of the curve, (2) Central or interior angle, and (3) Length of the arc. Other information, such as tangent distance, chord, and chord bearing, are helpful for layout and checking purposes.
The answer may not be what you think. In order to answer this question, you will have to understand the difference between the true geographic north and magnetic north. Because these two north locations are completely different….via Magnetic North vs Geographic (True) North Pole – GIS Geography