[libgweather/ebassi/docs-add-locations] docs: Port the "adding locations" section from the wiki

[Emmanuele Bassi <ebassi src gnome org>]

commit ab9c0885020115314a22d223ba3e92d4e5bfa68d
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Nov 11 15:31:57 2021 +0000

    docs: Port the "adding locations" section from the wiki
    
    It's probably more useful to have this text in the API reference and the
    repository, than on the wiki.

 doc/adding-locations.md | 164 ++++++++++++++++++++++++++++++++++++++++++++++++
 doc/libgweather.toml.in |   1 +
 doc/meson.build         |   1 +
 3 files changed, 166 insertions(+)
---
diff --git a/doc/adding-locations.md b/doc/adding-locations.md
new file mode 100644
index 00000000..99f71967
--- /dev/null
+++ b/doc/adding-locations.md
@@ -0,0 +1,164 @@
+Title: Adding new locations
+
+# Adding new locations
+
+## What are locations
+
+Libgweather contains information about:
+
+- major cities in each country
+- timezones for those cities as well as countries
+- [METAR](https://en.wikipedia.org/wiki/METAR) weather stations, attached to
+  airports
+
+For cities which aren't in the list, and if you're connected to the Internet,
+libgweather also uses OpenStreetMap's Nominatim service to search for
+locations.
+
+The locations are stored inside the `Locations.xml` file in the libgweather
+source code. Always check whether your city, METAR weather station/airport, or
+timezone is already in there.
+
+## What do we want in libgweather
+
+Ideally, libgweather would contain a list of all the more important cities in
+each country, with a METAR weather station/airport near it listed, so that
+accurate current weather can be fetched, and timezone or world clocks
+configuration can be done offline, without the need to resort to online
+databases.
+
+If you live in a specific country, you can probably better understand the
+expectations of users of that country when it comes to having their nearest
+"big city" listed. We usually prefer to only list cities with at least 100
+thousand inhabitants, but it's not a hard limit when it makes sense.
+
+Note that METAR weather stations/airports aren't the only weather stations that
+we know how to query, so don't worry if you can't find one.
+
+## Contributing
+
+You've already looked in the `Locations.xml` file, and in the project's
+[open issues](https://gitlab.gnome.org/GNOME/libgweather/issues) and
+[open merge requests](https://gitlab.gnome.org/GNOME/libgweather/merge_requests),
+and the timezone is incorrect, the weather can't be fetched, or your city isn't
+listed.
+
+First, try to find if something changed. For example, the country's timezone
+changed recently, or an airport closed, and collect those references. Our go-to
+reference is usually Wikipedia, because it usually references sources either in
+English or other languages.
+
+Possible references are:
+
+- [List of timezones](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones)
+- [List of airports by ICAO code](https://en.wikipedia.org/wiki/ICAO_airport_code)
+- [List of FIPS country codes](https://en.wikipedia.org/wiki/List_of_FIPS_country_codes)
+- [List of ISO country codes](https://en.wikipedia.org/wiki/ISO_3166-1#Current_codes)
+
+All done? Onto the next part
+
+### I don't know XML, I don't have time
+
+Simply tell us about the problem, and give us as much information as possible
+in [a new issue](https://gitlab.gnome.org/GNOME/libgweather/issues/new). Make
+sure to include links to explanation if at all possible. It's easier for you to
+know that a city is misnamed if you live there, but we want to be sure we're
+not making mistakes, because that would be quite frustrating.
+
+### I know XML at least a little
+
+If you know git, you probably know how to contribute Merge Requests and all
+that, so carry on to the next section.
+
+For the others, open the text file editor. Once you've made your changes to the
+file, you'll need to change:
+
+- the first line of the commit message to "locations: [summary of the changes]"
+- on the subsequent lines, add more explanation if any is needed, and all the
+  links to justify your change
+- choose a descriptive name for the "Branch name". We usually prefer lower-case
+  names with no spaces.
+
+And click "Commit changes". Congratulations on making libgweather better!
+
+For more information and examples, you can also check the [project's
+contribution guide](https://gitlab.gnome.org/GNOME/libgweather/-/blob/main/CONTRIBUTING.md).
+
+### Potential problems with changes
+
+We run a battery of automated tests on changes made to the `Locations.xml`
+file, to avoid problems on the more than 8000 locations it contains. Here's a
+list of potential problems we might run into:
+
+- the city is too small. If it has less than 100 thousand inhabitants, we might
+  want to accept it anyway if it is the capital of a state/region in the
+  country, and no bigger cities are around that people would usually search
+  for.
+- the airport is too far from the city. We have the coordinates for both the
+  city and a number of airports. If there's no airport listed, we'll try to
+  find the closest one in the same country. This is useful if you have 2 big
+  cities close to each other, but a shared airport.
+- the METAR weather station doesn't transmit data to the weather service we
+  use. Don't worry about it, include the airport, and we'll figure it out.
+- the coordinates are invalid. libgweather expects the coordinates to be
+  decimal, with a space separating them. On most Wikipedia pages, there will be
+  a link to the GeoHack website which will have the decimal value. Don't
+  forget to remove the "," and make sure you copied the "-" signs if they're
+  there!
+
+Other than that, if in doubt, include the information you're unsure about, and
+look around in the file for examples.
+
+## Further maintenance
+
+Want to help more? Pick a country, one you know well would be best, and look at
+the definitions.
+
+- Is every city name correct? (ie, it's the real name of a real city which is
+  actually in that country, not some other country.)
+- For cities known by multiple names:
+  - If the city is known by a different name in English than it is locally, is
+    it listed by its English name, with a comment indicating the local name?
+  - If the city is known by multiple names locally, are there comments
+    indicating the other local names? (Note that we're mostly only interested
+    in local names; it's generally not interesting to have comments giving
+    alternative foreign names for the city, except in the case of cities like
+    Gdańsk/Danzig or Kaliningrad/Königsberg that have very conspicuously
+    changed names over the centuries.)
+  - For cities with multiple local names but no English-specific name, are we
+    using the right local name as the "English" version? (Eg, since our dataset
+    has both Finnish and Swedish names for many cities in Finland, we have to
+    explicitly tell it to use the Finnish names. There may be other countries
+    that have this problem as well.)
+- Likewise, for countries that are divided into `<state>`s, are the `<state>`
+  names correct? (Basically all the same issues as the city names above apply
+  here.)
+  - Also, are all cities in the correct `<state>`?
+  - One known issue with the handling of `<state>`s: we can't currently deal
+    with cities that are considered to be their own state-level entities (eg,
+    Beijing, China or Berlin, Germany); For now, those cities need to be placed
+    inside imaginary `<state>`s of the same name. This will eventually be
+    fixed.
+- Is the use of transliteration / diacritic marks correct and "good"? In some
+  cases we're stripping out diacritic marks to make the names more
+  English-like. (Eg, the source dataset has all sorts of macrons and hooks and
+  stuff in its transliterations of Arabic names, so that "Riyadh" beomes
+  "Riyāḑ", etc. We flatten those back down to ASCII.) It might be the case that
+  in some countries we're stripping out diacritics that we should be leaving
+  there. (Or vice versa, maybe we're leaving in diacritics that should be
+  skipped in the English versions?)
+
+And onto the harder stuff:
+
+- Does each city and each METAR weather station location have the correct
+  coordinates?
+  - Cities are easy (but time-consuming) to verify; just search for the
+    coordinates in Google Maps. (The coordinates listed don't need to be the
+    exact coordinates of the city center, just something reasonably close.)
+  - Weather stations are harder; if the weather station is an airport, you can
+    often tell that the coordinates are correct because you can see the
+    airport's runways in the Google Maps satellite view. Other than that, if
+    the station is named after a city or geographic feature, you can at least
+    check that it really is near that feature. (In particularly egregious
+    cases, you can tell that the coordinates must be wrong because they place
+    the weather station in the ocean, or in the wrong country...)
diff --git a/doc/libgweather.toml.in b/doc/libgweather.toml.in
index 12822dc2..0abc9ae7 100644
--- a/doc/libgweather.toml.in
+++ b/doc/libgweather.toml.in
@@ -31,6 +31,7 @@ base_url = "https://gitlab.gnome.org/GNOME/libgweather/-/blob/HEAD/";
 [extra]
 urlmap_file = "urlmap.js"
 content_files = [
+  "adding-locations.md",
   "migrating-3to4.md",
 ]
 
diff --git a/doc/meson.build b/doc/meson.build
index 419f9790..aca24827 100644
--- a/doc/meson.build
+++ b/doc/meson.build
@@ -17,6 +17,7 @@ if get_option('gtk_doc') and get_option('introspection')
   )
 
   gweather_content_files = [
+    'adding-locations.md',
     'migrating-3to4.md',
   ]