Added initial database documentation

Adds basic documentation about the OBM-Buildings database.

\approve @ds \fyi @cnievas @nicgar

README.md

@@ -4,6 +4,62 @@ This repository handles the structure and migrations in the `obm_buildings` data
 
 The database is described through sql files in the `migrations/` directory.
 
+## Connection
+
+* $ `psql -h hayabusa.gfz-potsdam.de -U consumer obm_buildings` (allows to access data read-only)
+* $ `psql -h hayabusa.gfz-potsdam.de -U contributor obm_buildings` (allows data manipulation)
+
+**Example database for tests**
+
+This is an empty database to be filled with edge cases, with the purpose of running tests for our scripts before rolling them out to the real OBM buildings database. You can access it through the following commands:
+
+* $ `psql -h hayabusa.gfz-potsdam.de -U consumer -p 5434 obm_buildings`
+* $ `psql -h hayabusa.gfz-potsdam.de -U contributor -p 5434 obm_buildings`
+
+**Alternative legacy database backup for reference**
+
+This is the legacy database, which we keep for reference to be able to deal with (i.e. understand) legacy code. We will eventually erase it. You can access it through the following commands:
+
+* $ `psql -h hayabusa.gfz-potsdam.de -U consumer -p 5433 gis`
+
+## Database tables
+
+* `obm_buildings` - Main OBM Buildings attributes
+
+These tables are going to be moved into [database-osmreplication](https://git.gfz-potsdam.de/dynamicexposure/openbuildingmap/database-osmreplication):
+
+* `planet_osm_line` - OpenStreetMap source data
+* `planet_osm_nodes` - OpenStreetMap source data
+* `planet_osm_point` - OpenStreetMap source data
+* `planet_osm_polygon` - OpenStreetMap source data
+* `planet_osm_rels` - OpenStreetMap source data
+* `planet_osm_roads` - OpenStreetMap source data
+* `planet_osm_update` - OpenStreetMap source data
+* `planet_osm_ways` - OpenStreetMap source data
+* `spatial_ref_sys` - PostGIS table including known spatial reference systems
+
+
+## OpenBuildingMap Building attributes
+
+The core of OpenBuildingMap are the following attributes in the `obm_buildings` table:
+
+```
+   column_name   |          data_type          
+-----------------+-----------------------------
+ osm_id          | bigint
+ z_order         | integer
+ geometry        | geometry(Geometry,900913)
+ building        | text
+ building_use    | text
+ building_levels | text
+ amenity         | text
+ occupancy       | text
+ position        | text
+ floor_space     | double precision
+ last_modified   | timestamp without time zone
+ area            | double precision
+```
+
 ## More information
 
 * [Database versioning best practices](https://enterprisecraftsmanship.com/posts/database-versioning-best-practices/)