I am working on an app that has an iPhone version as well as an Android version.
My goal is...
you should consider following possible issues.
If application keep on sending user's location then the user battery will getting down, and web server memory will increase.
Application will keep on use internet to send location to web server.
At the time of roaming internet data cost may increase.
my suggestions:
The app should send the user's location every 15 minutes.
Every application should use unique id to update their location.
If application closed then clear that app's location in web server.