I am working with 2 shapefiles. One contains the boundaries of a city, the other contains polylines representing the topographic features of the area. Essentially, the polylines make a topographic map.
I want to calculate the average elevation of the city. I have some basic GIS knowledge, so I can select out just the polylines in the city... but I'm not sure how to determine the city's average elevation using this data? I could average the polylines together controlling for their length, but that's not quite accurate - a long line that goes around a lake contains a lot more area at the same elevation than a long line that goes around a big hill, for example.
Suggestions on how to do this?