Due to the API-change, this option does currently not work reliably. Please use areascan.
When doing a spawnscan, the client will query the Pokemonradar database for all spawnpoints in your areas that have a predicted spawn time. It will then scan each point one minute after the predicted spawn.
This method does save a lot of unnecessary scans and thus allows for much more or bigger areas with much less accounts. However, it might miss spawnpoints that have not previously been scanned often enough to make a reasonable spawn-time prediction.
The area scan will scan the entire area as fast as it can. This is useful to scan an area for spawnpoints, if the spawnscan is missing spawns.
If you run an areascan with an interval of maximum 12 minutes for at least an hour, all spawnpoints for your areas will be added to the Pokemonradar database. You can then stop the scan, and switch to use spawnscanning.