I'm digitizing a contour map to create a DEM, but there is a mine, and I'm a bit confused about it, I don't know how to digitize this. There are different numbers (e.g. -62), that I think about the loss of the elevation, but there are more numbers that belongs to one line. Any idea?
Here is a pic about the site: [ATTACH=CONFIG]21977[/ATTACH]
I see the confusion in this map and unfortunately no direct way of solving it except to understand what the hatched lines and numbers represent and at least be able to visualize what I would interpret as as a shallow pit though there are dumps east of the highway on the right.
The map shows a slope with contours between 1500 and 1800 (presumably feet) with superimposed hatched lines representing the crest or edges of mining benches I see cut into the hillside judging from the way contours are chopped. The numbers represent the height of the bench: -ves referring to the drop from the crest to the bench below. The one at the very left/top -57) is on the left side of the line away from the hatches as are all the other -ve. The +ve number is at the base of a cut and represents the rise to the crest.
As you can see the series of numbers through the middle of the benches add up to about the slope difference of the contours or 300 feet (or meters) so they are the same units. The problem is that the bench heights are variable along their length as shown by the changes in numbers so cannot be treated as contour lines although some connect directly to a contour. This is most evident and expected ones are at the top and bottom of the pit and in between less so (e.g. the -57 line runs to lower numbers to the south. If it could be simplified to assume that the crests at least in the middle of the pit were contours then the contours above could simply be crowded close together into the hatched area.
The other test is to compare how the crest heights intersect contours on the north side and south side of the pit and see how close they are. They are chopped in the image so I can't tell. The crest elevations can be expected to be fairly even and on contour, but all depends on the era in which the mining was done and hence the survey control.
What I would suggest is pick a few benches where the crest height looks even in the middle of the pit, check their north and south contour intersections and draw from there assuming even elevations. If the crest changes in elevation then you lines are going to cross the crests and that is harder to draw your contours, but at least you can visualize it.