We recently completed a drone survey in Amuwo-Odofin, Lagos for a client who wanted to see all the roads that connect to their off-dock container depot and their dimensions. While analyzing the final orthomosaic (georectified images stitched together to form one seamless image) we realized that if we were looking for vacant lands of a certain size to serve as depots (they need more space), this same survey would suffice.
A drone can be used to find vacant lands in an area. For example, if you are looking for vacant lands which are at least 3000 sq. mts., all you need to do is a drone survey that will cover your location of interest.
A drone survey is different from a regular drone image capture. The difference between them is that in a regular drone image capture, in most cases, you just capture the images and download them but in a drone survey the images are geometrically corrected (dimensions of features will be correct) and stitched together to form a single image called an Orthomosaic. Since the image is geometrically corrected, you can measure distances, areas, and volumes on the images with great accuracy.
After the drone survey, you will have the orthomosaic of the area. Now, all you have to do is import it into QGIS/ArcGIS/AutoCAD/Global Mapper or any other GIS or CAD software of your choice then you can use visual inspection to identify vacant lands and start measuring them to see which ones are at least 3000 sq. mts. If your area of interest is quite large and you are skilled enough, it will be better to do a Supervised Classification to identify all the vacant lands automatically.