@dilmandila How openstreetmap gets its data -> volunteers (maybe you ! definitely me) from all over the world collaboratively map whatever they want. Some people really like mapping footpaths ! As for the "how" the mapping is done for footpaths, it is either through the use of satellite imagery or on the ground information, as one prefers
Here's a beginner guide if you are interested :)
https://wiki.openstreetmap.org/wiki/Beginners%27_guide