> db.zips.find({city: "NEW YORK"}).explain()
{
	"cursor" : "BtreeCursor city_1",
	"isMultiKey" : false,
	"n" : 40,
	"nscannedObjects" : 40,
	"nscanned" : 40,
	"nscannedObjectsAllPlans" : 40,
	"nscannedAllPlans" : 40,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"city" : [
			[
				"NEW YORK",
				"NEW YORK"
			]
		]
	},
	"server" : "localhost:27017"
}

db.runCommand({ aggregate: "zips", explain: true, pipeline: [ {$match: {city: "NEW YORK"}} ] })
{
	"stages" : [
		{
			"$cursor" : {
				"query" : {
					"city" : "NEW YORK"
				},
				"coveredIndex" : false,
				"cursorType" : "BtreeCursor city_1"
			}
		}
	],
	"ok" : 1
}