1. A method comprising: constructing an index of sensors; clustering sensors together to form groups of sensors in a hierarchal structure, wherein the formation of the groups of sensors is based on at least one or more criteria including: sensor type, sensor location, and sensor schema; responsive to a query requesting sensor data, identifying via the index a random subset of sensors, from the groups of sensors, from which to collect the sensor data, wherein the random subset of sensors exhibits a spatial distribution similar to that of a full set of the sensors, wherein the identifying comprises: ascertaining a target size of a number of sensors to be read; splitting the target size into smaller portions; and distributing the smaller portions across the index of sensors; and obtaining the sensor data from the subset of sensors, wherein the sensor data includes sensor readings and metadata, the metadata comprising a schema that defines how the sensor readings are formatted.