The scanning API provides client location services...
https://developer.cisco.com/meraki/scanning-api/#!introduction/scanning-api
You need a server to take the data stream, capacity depends on the volume of location data to be processed - about 6-7 years ago I remember using a Raspberry Pi to run a live device/heatmap for a demo at an event, it was ok up to a few hundred clients. There're also cloud-based services available that use this API to do much of the work for you.
Real-world accuracy is heavily dependent on the RF environment.