On two types of suggestions

Basic overview of two types of search suggestions: content && search query based suggestions.

https://www.searchblox.com/autosuggest-search-query-based-vs-content-based

Spatial search algorithms and data scructures

https://medium.com/@agafonkin/a-dive-into-spatial-search-algorithms-ebd0c5e39d2a

How to deal with the synonyms. Awesome examples

http://opensourceconnections.com/blog/2016/12/02/solr-elasticsearch-synonyms-better-patterns-keyphrases/

Visualizing Geohash

I've rescued a lost article on visualizing geohashes

Good explanation of how the DisMax works (despite that it based on Solr, but not my favorite Elasticsearch)

http://opensourceconnections.com/blog/2013/03/07/the-anatomy-of-a-dismax-query/

There you can find some useful ideas how to combine search and graphs together to improve your relevance.

http://blog.comperiosearch.com/blog/2014/02/05/dynamic-search-ranking-using-elasticsearch-neo4j-and-piwik/ 

Very interesting article that has a link on the interesting tool.