In-Ground systems require room for the concrete footer. The dimensions of the footer are different for different models. For example, the smallest footer would be for APOLLO 60 and 54 at 16" square vs the largest THOR Diamond at 24" square. Adjustable systems also require room behind the pole to allow for the adjustment mechanism. This also varies by model but is usually about 17 inches.
Portable systems in contrast to in-ground have all of their support above ground. The footprint for these will be larger. For example, on the BEAR portable, the required footprint is 66" deep by 40" wide.
Roof-Mount basketball hoops may not be on the ground but they do need space on the roof to mount the bracket. The ROOF KING bracket is 20" wide, 32" deep. There are also requirements on the roof height to ensure you can get the rim to a regulation 10' height. See the ROOF KING's installation requirements.
Wall-Mount hoops, again, are not on the ground but do need enough room on your wall. The WALL KING bracket requires 44" vertically. There are also other requirements you can see here.
Lastly, another thing to consider when thinking about space requirements is the basketball system's overhang defined as the distance from the post or base to the backboard. This is how far the backboard is projected into your playing area. If you have a shallow playing area without room to set the post or base off the playing area, the backboard can be projected too far eliminating many shots in front of the backboard.