Finding area/volume under a 3d plot

Hello,

I have some data that can be looked at in 2d and in 3d. In 2d, it's typical to look at the area under the plotted "curve" and I can easily do that using the trapz function. For example, if my plot is x = [1 2 3] and y = [10 20 30] then trapz(x,y) correctly gives me the area under the plotted line as 40. However, let's say I also have a dimension Z = [10 10 10], then, I would think integrating that space under the plot should result in something like 400? (my math could be wrong).

Currently, my data is in the format that has 3 rows and 25 columns (5 values for X by 5 values for Y) : [0 0 0 0 0 1 1 1 1 1... 5 5 5 5 5; 1 1 1 1 1 2 2 2 2 ... 10 10 10 10 10; 200 150 120 80 10... 40 30 20 10 0]

I have looked through various questions that seem similar to this, but couldn't quite get the solutions to work for me. For instance, I think this is probably the right direction, but I am still stuck: I think this post is related: https://blogs.mathworks.com/loren/2011/06/13/calculating-the-area-under-a-surface/#1

In short, I'm trying to find some empirical way to demonstrate if the area/surface under one plot is smaller than under another plot, and perhaps (eventually) if the plot slopes down as x and y increase. I am sure there are other ways to describe the data, but there is already an established "area under the curve" measure for 2d plots, and I wonder if it could be sensible to have an analogous measure for 3d plots.

Thank you!!