Clarify SETUP_DATABASE

SETUP_DATABASE.md

@@ -15,23 +15,35 @@ osm2pgsql
 # Setting up PostreSQL
 ```bash
 initdb -D data
+
+# Start the database server; leave this running and contiue in another
+# terminal:
 postgres -D data
+
 createdb gis
 psql -d gis -c 'CREATE EXTENSION postgis;'
 ```
 
-# Transforming data
-Schema reference: https://wiki.openstreetmap.org/wiki/Osm2pgsql/schema
+# Filling the database with osm data
+Use one of the following two code blocks to get started. When everything
+worked out, you can start playing around with bigger `*.pbf` files,
+like Sweden, the USA or even the whole planet. You can find those at
+[download.geofabrik.de](https://download.geofabrik.de) and
+[planet.osm.org](https://planet.osm.org).
 
+Azores (nice and small; good for quick testing):
 ```bash
-# Download the osm data:
 wget 'https://download.geofabrik.de/europe/azores-latest.osm.pbf'
-wget 'https://download.geofabrik.de/europe/serbia-latest.osm.pbf'
 
-# Takes ~30s; turns the ~10MB into ~300MB:
+# Takes ~30s; turns the ~10MB *.pbf file into a ~300MB database:
 osm2pgsql --create --database gis azores-latest.osm.pbf
+```
 
-# Takes ~15min; turns the ~100MB into ~3.9GB:
+Serbia (a little bigger, but still good for testing on a simple laptop):
+```bash
+wget 'https://download.geofabrik.de/europe/serbia-latest.osm.pbf'
+
+# Takes ~15min; turns the ~100MB *.pbf file into a ~3.9GB database:
 # --number-processes 1 seems to be necessary since max_connections in
 # data/postgresql.conf is limited to 20 on OpenBSD.
 osm2pgsql \
@@ -43,7 +55,12 @@ osm2pgsql \
 	serbia-latest.osm.pbf
 ```
 
-# Example queries
+# Example queries (you can skip this)
+To make sure everything works, you can use queries like the following
+ones. Enter these into a PostreSQL shell. Such a shell can be opened
+with `psql -d gis`. Make sure the PostreSQL server is running
+(`postgres -d data`).
+
 Finding cinemas in Belgrade:
 ```sql
 SELECT osm_id, name FROM planet_osm_point
@@ -57,3 +74,5 @@ SELECT osm_id, name, ST_AsText(ST_Transform(way, 4326)) FROM planet_osm_point
 WHERE shop = 'bicycle'
 AND way && ST_Transform(ST_GeomFromText('POLYGON((8.7968 53.1037, 8.8142 53.1037, 8.8142 53.0834, 8.7968 53.0834, 8.7968 53.1037))', 4326), 3857);
 ```
+
+Schema reference: https://wiki.openstreetmap.org/wiki/Osm2pgsql/schema