Google App Engine NDB Query on Many Locations
You didn't say how frequently the data points are updated, but assuming 1) they're updated infrequently and 2) there are only hundreds of points, then consider just querying them all once, and storing them sorted in memcache.  Then your handler function would just fetch from memcache and filter in memory.
This wouldn't scale indefinitely but it would likely be cheaper than querying the Datastore every time, due to the way App Engine pricing works.
I am developing a web app based on the Google App Engine. 
It has some hundreds of places (name, latitude, longitude) stored in the Data Store. 
My aim is to show them on google map. 
Since they are many I have registered a javascript function to the idle event of the map and, when executed, it posts the map boundaries (minLat,maxLat,minLng,maxLng) to a request handler which should retrieve from the data store only the places in the specified boundaries.
The problem is that it doesn't allow me to execute more than one inequality in the query (i.e. Place.latminLat, Place.lntminLng).
How should I do that? (trying also to minimize the number of required queries)