Civil Drafting Technology

Civil Drafting Technology Chapter 7 Location and Direction

Figure 7–1: Measuring longitude.

Table 7-1: Length of a degree of longitude

Figure 7–2: Measuring latitude.

Figure 7–3: Using coordinates of parallels and meridians to find locations.

Figure 7–4: Finding the distance between point A at 30° north latitude, 110° east longitude, and point B at 42° north latitude, 110° east longitude.

Figure 7–5: Finding the distance between A at 22° south latitude, 65° west longitude, and point B at 22° south latitude, 79° west longitude.

Figure 7–6: If the points are fairly close, such as a few hundred miles or less from each other on a different longitude and latitude, you can image the surface of the earth as being flat and use the Pythagorean theorem to find distance.

Figure 7–7: The hypotenuse is the longest side of a right triangle, apposite the 90° angle. A right triangle has one 90° angle.

Figure 7–8: Using the Pythagorean theorem formula, a2 + b2 = c2, to calculate the distance between paints A and B, where a and b are sides of the right triangle and c is the hypotenuse, which is the distance between points A and B.

Figure 7–9: A spherical triangle is shown on the earth’s surface between points A, B, and C. Notice how the sides a, b, and c of the spherical triangle are arcs rather than straight lines, as discussed when using the Pythagorean theorem and shown in Figure 7–8.

Figure 7–10: (a) Mariner’s and (b) surveyor’s compass.

Figure 7–11: Azimuth.

Figure 7–12: Bearing.

Figure 7–13: Examples of (a) bearings and (b) bearings and equivalent azimuths.

Figure 7–14: Sample of magnetic declination.

Figure 7–15: UTM grid and 1994 magnetic north declination at center of sheet.

Figure 7–16: Magnetic declination changes throughout the United States. (Courtesy of the National Geophysical Data Center, NGDC)

Figure 7–17: Formulas used to calculate true azimuth, given magnetic azimuth and magnetic declination.

Figure 7–18: A portion of a quadrangle map providing location and direction.

Figure 7–19: All angles of a four-sided polygon will equal 360° when added.

Figure 7–20: Opposite angles of intersecting lines are equal.

Figure 7–21: Example of a typical traverse. Included angles and distances are given.

Figure 7–22: Calculating bearings: line BC.

Figure 7–23: Calculating bearings: line CD.

Figure 7–24: Calculating bearings: line DA.

Figure 7–25: Bearings and distances shown on a plat.

Figure 7–26: Rough sketch of a plat.

Table 7–2: Plotting table

Figure 7-27: Error of closure.

Figure 7–28: Correcting the error of closure.

Figure 7–29: Closed traverse.

Figure 7–30: Positive and negative latitude.

Figure 7–31: Positive and negative departures.

Figure 7–32: A right triangle created by property lines with latitude and departure.

Figure 7–33: Setting up a table for latitude and departure calculations.

Figure 7–34: Plot information processed by a computer automatically calculates and balances latitudes, departures, and azimuths.

Civil Drafting Technology