Which graph database for search engine and gis?
Well you could use IBM DB2 LUW (Linux,Unix, Windows) Express-C edition. It is free and has community support. It is the same engine/binaries as DB2 Enterprise Edition, it just has certain features "turned off" and has memory and CPU caps, but for what you are describing, it may suit your needs. If you do find you need more memory/CPU you could always purchase a license from IBM to upgrade it to Express or one of the higher editions.

There is an add on called DB2 Spatial Extender, which has functionality for geo-spatial analysis. According to this chart here, it should be free to download and use, even with Express-C edition. You can download DB2 Spatial Extender here. And here is the Information Center documentation on DB2 Spatial Extender. Use the table of contents to browse.