if you go from one point to the other do you subract the a and b or do you do all points in between to find the elevation?
I'm not sure what this question refers to. Are you trying to calculate slopes?
Yes, I can help you with that. To calculate slopes or elevation changes between two points, you generally subtract the elevations of the two points. You don't need to consider all the points in between unless you specifically want to analyze the elevation changes at each intermediate point.
If you have the elevation values for point A and point B, you can subtract the elevation of point A from the elevation of point B to find the elevation change. If the value is positive, it means there is an increase in elevation from point A to point B. If the value is negative, it means there is a decrease in elevation.
However, it's worth mentioning that if there are significant variations in elevation between the two points, considering intermediate points might provide a more detailed analysis of the slope, especially if you're looking to measure changes over a relatively long distance. In such cases, you can divide the total change in elevation by the horizontal distance between the two points to calculate the average slope.