Added on version 2.1.7
If you intend to have a website with thousands of listings on a map, then you will definitely need a server with very high PHP max memory. By default 400 businesses are loaded in a map on every request, but if you have a very good server and want to increase this number, there is an option for this. Go to Toolkit Options > Business Settings > Number of loaded businesses on map
Lets say you increase this number to 1000. Then on every request 1000 listings will be added to the map, but this may come on expense of your maximum PHP memory. If you see a PHP memory max reached error, then you need to decrease this number or increase your PHP memory by getting a better server.