1. English Wikipedia. www.wikipedia.org.
2. Geohash.org. www.blog.labix.org/2008/02/26/geohashorg-is-public.
3. Geopoint Field Type in ElasticSearch. www.elastic.co/guide/en/elasticsearch/reference/current/geopoint.html.
4. Geospatial Indexes in MongoDB. www.mongodb.com/docs/manual/core/geospatial-indexes/.
5. The New York Times - On This Day. www.learning.blogs.nytimes.com/on-this-day/.