Heightfield from Image

I’m having trouble with the “Heightfield from Image” function in the mac version. I’m new to Rhino so I assume its user error, however it doesn’t seem to be working the way I expect. I watched this tutorial and found the same image he is using ( size of image is possibly not the same as in the tutorial) and even if I set my height to 50 meters ( his is at 2000) the variations in height are enormous. I’m using the preset for large object in meters. I also tried enlarging the grid to fit kilometers but still was way to dynamic in the height.

I tried a lot of different settings and images but have yet to get a single clean or even usable map from this function. If I’m doing something wrong is there a more detailed tutorial about how to use this feature?
Thanks. I’m also using Rhino 5.1 for Mac.

I figured it out. I was on the right track. I just didn’t make the grid size large enough. I needed it to be in kilometers. Once I made the grid spacing and size large enough the outcome looked quite similar.