# Spacings in contours? WHat does that mean?

1. Sep 24, 2011

### flyingpig

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

[PLAIN]http://img683.imageshack.us/img683/4584/unledjotq.png [Broken]

3. The attempt at a solution

For a) I just did F(0.4, 1) = 148.77, which was wrong...

Last edited by a moderator: May 5, 2017
2. Sep 24, 2011

### SammyS

Staff Emeritus
Doesn't curve (a) pass through the origin?

What is f(0, 0) ?

3. Sep 25, 2011

### flyingpig

150 - 0 = 150

4. Sep 25, 2011

### Redbelly98

Staff Emeritus
Don't stop there, continue on with solving the problem.

5. Sep 25, 2011

### flyingpig

i tried doing b) using my old method

f(0.4,0) = 150e^(0.4) = 224

Not right

I still don't understand the whole "5 spacing"

6. Sep 26, 2011

### Redbelly98

Staff Emeritus
Looks right to me, maybe just a rounding-off issue. You could always see if that contour crosses some other grid point, and calculate the function there.

I have no idea what that means, sorry.

EDIT: does "5 spacing" refer to something your professor said? Or was it in the portion of the problem statement that was cut off in your original post?

Last edited: Sep 26, 2011
7. Sep 26, 2011

### HallsofIvy

Staff Emeritus
Have you ever used a "geodetic map"? Those are maps that show, in addition to highways and towns, hills, trails, etc. so are used by hiker, hunters, and the like. They are called geodetic maps because they also show "geodetic levels", lines of constant altitude. That is precisely what contour maps are: the lines show constant height of the three dimensional figure at two dimensional (x,y) points. Since the contour lines, like the geodetic lines, are shown at a constant interval of height, if two lines are close together, that means you have to go up that distance in a short horizontal distance. If two lines are farther apart you have to go up that distance in a longer horizontal distance. In other words, the closer contour lines are together the steeper the slope is there. On a geodesic map, lines that are far apart means a nice gentle slope, line that are very very close together means a cliff!

8. Sep 26, 2011

### SammyS

Staff Emeritus
That gives an a to b spacing of 74.

Also, try f(0.6, 0.8)

Pick a point or two for c & d. Then try to find a 'nice' number that can be used for equal spacing & which approximately works for the numbers you get for contours a, b, c, d.

9. Sep 26, 2011

### flyingpig

f(0.6,0.8) doesn't touch anywhere

10. Sep 26, 2011

### Staff: Mentor

f(.6, .8) is on the contour labeled b.

11. Sep 26, 2011

### flyingpig

Yeah I just saw that lol, I was looking at (0.4,0.8)

12. Sep 26, 2011

### flyingpig

f(0.6,0.8) = 225 roughly...

13. Sep 26, 2011

### flyingpig

Okay I managed to knock out b) and c) with 225 and 300 respectively. for d) I got 370...which is wrong.,

14. Sep 26, 2011

### Redbelly98

Staff Emeritus
Now that you've evaluated contours a and b, it looks like you have enough information to complete the problem.

However, I do wonder about the part of the problem statement you have omitted from your original post. I.e., "They are equally" is not a complete sentence.

15. Sep 26, 2011

### flyingpig

omg it was cut off? It was "They are equally spaced multiples of 5"

omg

16. Sep 26, 2011

### flyingpig

I just poisoned myself with this problem...

17. Sep 26, 2011

### Redbelly98

Staff Emeritus
Well, I asked about this as early as Post #6. At any rate, the key phrases are "equally spaced" and "multiples of 5".

The phrase "multiples of 5" indicates why your previous answers of 148.77 and 224 were obviously wrong, and what their values probably are without having to evaluate the function at additional points.

The phrase "evenly spaced" tells us why your answer of 370 is wrong, and what the correct answer should be for contour d.

Now that all the information you need has been spelled out, I shall close this thread and let you finish solving it. Please be more careful in posting problem statements in the future.