From Openkore Wiki
Map routing weights for maps that Kore is walking through to reach the destination.
The format of this file is simply a set of lines that observes the following syntax:
<map name> <weight>
- <map name>
- This is the name of a map as shown by the where command in Kore, or the /where command in the original client. For example: prontera, morocc, prt_fild08, etc.
- This is a number (can be negative) that specifies additional steps that Kore would think it has to walk through inside the map aside from the actual calculated route distance.
Kore generally tries to use the shortest path to get to the desired destination map. The path is counted in number of steps (tiles) the character would have to walk. Map routing weights can be seen as additional steps that Kore thinks it would have to do on a specific map. Positive weights makes Kore avoid a map; negative weights makes it prefer a map.
The following example, will make Kore avoid walking through prt_fild08, as long as there is an alternative path that has not more than 500 additional steps. Therefore you could say Kore prefers to walk up to 500 additional steps rather than walking through prt_fild08.
Using a weight of 10000 makes it pretty sure to completely avoid a map.