# Partial derivatives of contour maps/level curves

1. Sep 20, 2010

### nlsherrill

1. The problem statement, all variables and given/known data

Basically I have two problems that are asking for the partial derivative with respect to x and y at a certain point on a level curve graph, and a contour map. How do you go about doing these? There is no function given, so I don't really know what they expect you to do. Theres also no examples at all in my book or from lecture notes.

2. Relevant equations

3. The attempt at a solution

So I know to leave y as a constant if im differentiating with respect to x and etc...but I just don't know how to calculate a tangent line in these situations. Any help/hints appreciated.

2. Sep 20, 2010

### slider142

I do not see how you can get accurate partial derivatives from a contour map. One method is to use the difference in elevations divided by the difference in y (or x). By the mean value theorem, this is the partial derivative for some value of y in the interval.

3. Sep 20, 2010

### nlsherrill

Well the problem says "estimate", but I figured since it's webassign that could mean just round off to the nearest whole number since the level curves/contour maps are given as just whole numbers.