Reading former issues here, I understand how you derived at your current Admin Level system implemented. #392 #398

And it all makes sense to a degree. It is clear that every country has different Admin Levels.

My issue takes place with locations within a certain country and their own Admin Level hierarchy and how to handle differences and inconsistencies. Let's take Germany for example since there has been a similar open discussion #483 . Here you can have cities with state, region and county but not necessarily. One city can have a region while the next one doesn't.

GeoNames therefore delivers empty admin_level_2 (Region) for those cities.

Look at "adminName2": ""

{"geonames": [{
  "adminCode3": "03458",
  "adminCode2": "00",
  "countryName": "Germany",
  "adminCode1": "06",
  "lng": "8.55947",
  "adminCode4": "03458005",
  "adminName2": "",
  "fcodeName": "populated place",
  "adminName3": "Landkreis Oldenburg",
  "distance": "0.82744",
  "timezone": {
    "dstOffset": 2,
    "gmtOffset": 1,
    "timeZoneId": "Europe/Berlin"
  },
  "adminName4": "Ganderkesee",
  "adminName5": "",
  "name": "Almsloh",
  "fcode": "PPL",
  "geonameId": 2958212,
  "asciiName": "Almsloh",
  "lat": "53.05641",
  "population": 0,
  "adminName1": "Lower Saxony",
  "adminId1": "2862926",
  "countryId": "2921044",
  "fclName": "city, village,...",
  "elevation": 0,
  "countryCode": "DE",
  "adminId4": "6552965",
  "adminId3": "2857455",
  "toponymName": "Almsloh",
  "fcl": "P",
  "continentCode": "EU"
}]}

This goes against previous comment @giosh94mhz #428

[...] In theory (and in all my tests), all providers properly fill Admin Level starting with one, and there are not holes (e.g. level 1 and 3 present, without level 2). [...]

Based on the above comment GeoNames implementation drops empty Admin Levels:

/src/Geocoder/Provider/Geonames.php#140

for ($level = 1; $level <= AdminLevelCollection::MAX_LEVEL_DEPTH; ++ $level) {
    $adminNameProp = 'adminName' . $level;
    $adminCodeProp = 'adminCode' . $level;
    if (! empty($item->$adminNameProp) || ! empty($item->$adminCodeProp)) {
        $adminLevels[] = [
            'name' => empty($item->$adminNameProp) ? null : $item->$adminNameProp ,
            'code' => empty($item->$adminCodeProp) ? null : $item->$adminCodeProp,
            'level' => $level,
        ];
    }
}

Which results in different Admin Level sets within the same country. Admin Level 2 may contain a region or maybe a county.

Another issue would take place when using OpenStreetMap as a provider. Here the Admin Level has been taken ad absurdum since for all countries only state and county are being imported.

/src/Geocoder/Provider/Nominatim.php#111

$adminLevels = [];
foreach (['state', 'county'] as $i => $tagName) {
    if (null !== ($adminLevel = $this->getNodeValue($addressNode->getElementsByTagName($tagName)))) {
        $adminLevels[] = ['name' => $adminLevel, 'level' => $i + 1];
    }
}

This way a lot of information is lost/unusable in most countries as you can see in the listing #392 .

How would I safely extract the county using GeoNames for Germany cities for example? Even though every city in German will have a county it will not always be at the same Admin Level.