Hi Vraukis,
Are the Objects (buildings?) on the same level? Then the surface which is supposed to be displaced should be a direct fit to them. The value of the displacement map should be then a mid gray, and “Intensity (Centered)”.
If you have then set up the Displacement “Height” to an value, the black and white of that gray map will reach this value in plus and minus. The Strength of course set to 100%. This works for Red/Green maps in a similar way expect that dark in each channel means no movement and white in red or green means 100% of the height setting. These two colors stand for up and down, speaking of floor level.
If they are all over the place in terms of height, try this:
If Sub-Polygon-Displacement is not needed, use the Displacer Object. This can help as well for a good preview. Note that you can adjust such height maps with the colorizer. Which allows as well to change jsut some leveles of the map, and leave others untouched. If you take an Top view rendering from you scene, you might adjust the map after doing the math for the object position.
Another way is based on cubes that you place on the floor level of the objects. Then place a flat projection of a gradient from the side, with black the lowest and white the highest point. The top view generates then (if the gradient is in the Luminance channel and anything else is off) a nice map to adjust you original map in Photoshop.
It’s a number game.
All the best
Sassi