The course of Sandy Creek indicates a long valley, extending almost the entire length of the map. Meadow Creek follows another valley, and Deep Run another. When these streams happen to join other streams, the valleys must open into each other.
[1867]. Map Distances (or horizontal equivalents). The horizontal distance between contours on a map (called map distance, or M. D.; or horizontal equivalents or H. E.) is inversely proportional to the slope of the ground represented—that it to say, the greater the slope of the ground, the less is the horizontal distance between the contours; the less the slope of the ground represented, the greater is the horizontal distance between the contours.
Fig. 10
| Slope (degrees) | Rise (feet) | Horizontal Distance (inches) |
|---|---|---|
| 1 deg. | 1 | 688 |
| 2 deg. | 1 | 688/2 = 344 |
| 3 deg. | 1 | 688/3 = 229 |
| 4 deg. | 1 | 688/4 = 172 |
| 5 deg. | 1 | 688/5 = 138 |
It is a fact that 688 inches horizontally on a 1 degree slope gives a vertical rise of one foot; 1376 inches, two feet, 2064 inches, three feet, etc., from which we see that on a slope of 1 degree, 688 inches multiplied by vertical rises of 1 foot, 2 feet, 3 feet, etc., gives us the corresponding horizontal distance in inches. For example, if the contour interval (Vertical Interval, V. I.) of a map is 10 feet, then 688 inches × 10 equals 6880 inches, gives the horizontal ground distance corresponding to a rise of 10 feet on a 1 degree slope. To reduce this horizontal ground distance to horizontal map distance, we would, for example, proceed as follows:
Let us assume the R. F. to be 1/15840—that is to say, 15,840 inches on the ground equals 1 inch on the map, consequently, 6880 inches on the ground equals 6880/15840, equals .44 inch on the map. And in the case of 2 degrees, 3 degrees, etc., we would have:
M. D. for 2° = 6880/15840 × 2 = .22 inch;
M. D. for 3° = 6880/15840 × 3 = .15 inch, etc.