(1)
How do the heights in the bmp work.
There is 6 rows across and lots of rows (50maybe ) down.
Is each 25 metre height a row down starting at top for 0m and down to bottom for 1250m?
And each row across just adds a little variation to picture for set height for that row?
In essence, yes, although you can set the height to be variable (you can have 2 metre or 100 metre contours if you want), my mapping standard is typically 25 metres.
The row of 6 is the same elevation, just slight variations in the hexes to "mix it up" usually a texture difference.
The 50 rows are from the lowest elevation to the highest elevation.