How to store information about the boundaries of the city in the database?

Question

Cartography

Hello.
There is a site catalog of sports facilities, which is still being developed (I'm not a programmer, I use the services of freelancers) I
plan to make a search for objects with the possibility of additional coverage of the territory around the city within the specified radius For example, as done on the
OLX.UA website ( screenshot )
at the moment there is a solution that I do NOT like myself (I repeat that I am not a programmer):

1. Determine the coordinate of the city center
   
2. Determine the coordinate of the farthest point of the border (it seems that you can pull it from OSM)
   
3. Measure the distance between them and the reference point, calculate the radius from the center to the farthest point
   

The option is bad because cities do not have round borders.
I would like to consult, is there a better way to implement this functionality?
Thank you.

Answer 1

If you are not using a spatial database, then it's time to switch to it.
Compares two geometries and checks if they are closer than the specified number of units - postgis.net/docs/ST_DWithin.html

Answer 2

mysql check if point is in polygon