Add new "explore" theme with some initial topics

OpenStreetMap contains an insane amount of complex data. If you want to
use some of that data a first step is often to explore what's there,
filter out the stuff that looks interesting, creating some experimental
maps, figuring out what's useable and how. The topics in this theme are
meant as starting points for such an exploration. They are intended to
be used with a tool such as QGIS to quickly display what's there in
different ways.

Initial topics are "coastline", "postcode", and "restrictions".

Author: joto

README.md

@@ -135,6 +135,18 @@ These are some experimental layers. Use at your own risk.
 
 [More...](themes/experimental/README.md)
 
+### Theme `explore`
+
+OpenStreetMap contains an insane amount of complex data. If you want to use
+some of that data a first step is often to explore what's there, filter out the
+stuff that looks interesting, create some experimental maps, figure out what's
+useable and how. The topics in this theme are meant as starting points for such
+an exploration. They are intended to be used with a tool such as QGIS to
+quickly display what's there in different ways. QGIS project files are provided
+as a starting point.
+
+[More...](themes/explore/README.md)
+
 ### Theme `external`
 
 This theme contains some layers not generated directly from OSM data but

config/explore_coastline.lua

@@ -0,0 +1,23 @@
+-- ---------------------------------------------------------------------------
+--
+-- Example config for exploring OSM data
+--
+-- Configuration for the osm2pgsql Themepark framework
+--
+-- ---------------------------------------------------------------------------
+
+local themepark = require('themepark')
+
+-- For debug mode set this or the environment variable THEMEPARK_DEBUG.
+themepark.debug = true
+
+-- ---------------------------------------------------------------------------
+
+themepark:set_option('debug', 'debug') -- Add JSONB column `debug` with debug infos in debug mode
+themepark:set_option('tags', 'all_tags') -- Add JSONB column `tags` with original OSM tags in debug mode
+
+-- ---------------------------------------------------------------------------
+
+themepark:add_topic('explore/coastline')
+
+-- ---------------------------------------------------------------------------

config/explore_postcodes.lua

@@ -0,0 +1,23 @@
+-- ---------------------------------------------------------------------------
+--
+-- Example config for exploring OSM data
+--
+-- Configuration for the osm2pgsql Themepark framework
+--
+-- ---------------------------------------------------------------------------
+
+local themepark = require('themepark')
+
+-- For debug mode set this or the environment variable THEMEPARK_DEBUG.
+themepark.debug = true
+
+-- ---------------------------------------------------------------------------
+
+themepark:set_option('debug', 'debug') -- Add JSONB column `debug` with debug infos in debug mode
+themepark:set_option('tags', 'all_tags') -- Add JSONB column `tags` with original OSM tags in debug mode
+
+-- ---------------------------------------------------------------------------
+
+themepark:add_topic('explore/postcodes')
+
+-- ---------------------------------------------------------------------------

config/explore_restrictions.lua

@@ -0,0 +1,23 @@
+-- ---------------------------------------------------------------------------
+--
+-- Example config for exploring OSM data
+--
+-- Configuration for the osm2pgsql Themepark framework
+--
+-- ---------------------------------------------------------------------------
+
+local themepark = require('themepark')
+
+-- For debug mode set this or the environment variable THEMEPARK_DEBUG.
+themepark.debug = true
+
+-- ---------------------------------------------------------------------------
+
+themepark:set_option('debug', 'debug') -- Add JSONB column `debug` with debug infos in debug mode
+themepark:set_option('tags', 'all_tags') -- Add JSONB column `tags` with original OSM tags in debug mode
+
+-- ---------------------------------------------------------------------------
+
+themepark:add_topic('explore/restrictions')
+
+-- ---------------------------------------------------------------------------

themes/explore/README.md

@@ -0,0 +1,101 @@
+
+# Theme `explore`
+
+OpenStreetMap contains an insane amount of complex data. If you want to use
+some of that data a first step is often to explore what's there, filter out the
+stuff that looks interesting, create some experimental maps, figure out what's
+useable and how. The topics in this theme are meant as starting points for such
+an exploration, they are intended for advanced OSM users.
+
+The data generated is intended to be used with an interactive tool such as QGIS
+to quickly display what's there in different ways.
+
+Some of these topics import quite a lot of data and do extensive
+post-processing, try with a smaller extract before you run them on the planet
+file.
+
+For some details on the contents of the generated database see the source
+code of the config file.
+
+## Naming
+
+All table names have the respective topic as prefix.
+
+## Updates
+
+Topics are mostly written in a way to allow updates of OSM data. But updates
+might take a while, so minutely updates are not possible for all of then.
+This should be improved upon.
+
+## Postprocessing
+
+Use `osm2pgsql-gen` with the respective config file to run SQL commands that do
+some postprocessing on the imported data. Without that some tables and/or
+columns will not be filled with data.
+
+## Optional Pre-Filtering
+
+For some topics it can make sense to pre-filter the OSM data, so that
+processing with osm2pgsql is faster. This is entirely optional. Each topic will
+show a command line using [Osmium](https://osmcode.org/osmium-tool/) that does
+this pre-filtering.
+
+## QGIS Config
+
+The `qgis` directory contains QGIS config files for each of the themes. They
+all use the [database
+service](https://www.postgresql.org/docs/current/libpq-pgservice.html)
+`explore`. Create a file `.pg_service.conf` in your home directory (if it is
+not already there) and add an entry like this:
+
+```
+[explore]
+host=localhost
+port=5432
+dbname=explore
+user=USERNAME
+password=PASSWORD
+```
+
+## Topic: Coastline
+
+Explore coastline tagging. Everything tagged `natural=coastline`.
+
+Coastline ways are shown, with details if zoomed in. Pseudo-coastlines along
+the 180° meridian and the South Pole that have special tagging are also shown.
+Coastlines can only be tagged on ways. Nodes and relations with tag
+`natural=coastline` are shown as errors. Coastline (self-)intersections and
+open ends are shown as errors as well.
+
+Pre-Filtering:
+
+```
+osmium tags-filter -o coastline.osm.pbf DATA.osm.pbf \
+    natural=coastline
+```
+
+## Topic: Postcodes
+
+Explore postcodes in OSM, on POIs, buildings, and from postcode boundaries.
+
+Also generates postcode areas from points using convex hull and Voronoi
+decomposition.
+
+Pre-Filtering:
+
+```
+osmium tags-filter -o postcodes.osm.pbf DATA.osm.pbf \
+    'addr:*' r/postal_code
+```
+
+## Topic: Restrictions
+
+Turn restrictions (relations tagged `type=restrictions`) for road navigation.
+
+Pre-Filtering:
+
+```
+osmium tags-filter -o restrictions.osm.pbf DATA.osm.pbf \
+    w/highway w/amenity=parking r/type=restriction
+```
+

themes/explore/init.lua

@@ -0,0 +1,11 @@
+-- ---------------------------------------------------------------------------
+--
+-- Theme: explore
+--
+-- ---------------------------------------------------------------------------
+
+local theme = {}
+
+return theme
+
+-- ---------------------------------------------------------------------------