Project array content with mongodb
You need to do an $unwind operator on the Location array first in your aggregation pipeline, then $group the resulting documents to apply the accumulator expressions $first and $last.
Your aggregation pipeline should look like this (untested):
db.foo.aggregate([ { "$unwind": "$location" }, { "$group": { "_id": "$_id", "longitude": { "$first": "$location" }, "latitude": { "$last": "$location" } } }]);