Gloss names of places in the local language

[1ec5]

World political maps and atlases by American publishers typically show well-known places in English but also gloss the name in the local language when it differs from the English name. Typically, the local name is shown in parentheses and/or italics, and sometimes on a separate line in smaller type.

I’ve seen these glosses on labels of populated places, but rarely on other kinds of features. I suppose there are a variety of reasons:

• Many anglicized city names are less well-known than official English names of countries.
• A waterway may form an international boundary and thus have a whole host of local names, but consistency along the length of the waterway is often prioritized.
• Labels for non-place POIs are already long enough to risk getting collided out by POI labels without getting doubled in length by the gloss.
• Political maps rarely label anything less significant than a populated place.

We should consider glosses for other feature types at higher zoom levels, where collision isn’t as much of a concern, but populated places seems like a good place to start.

To achieve the gloss, we can set text-field to a format expression that includes both name:en and name when the two properties differ. A collator expression can be passed into the string comparison to perform case and diacritic folding.

/ref #100 #428

[1ec5]

The ability to choose a base language other than English (#20 #21) would complicate this feature somewhat, but even in English there are some edge cases to consider:

• Since “Montreal” and “Montréal” differ by only diacritics, it’s probably fine to render it as just “Montréal” instead of “Montreal (Montréal)”.
• Hong Kong’s place name labels are bilingual in both English and Chinese, so the expression would need to avoid duplicating the English name. For example, it should be “Kowloon (九龍)”, not “Kowloon (九龍 Kowloon)”.

[1ec5]

For local names written in non-Latin writing systems, National Geographic and Rand McNally show romanizations rather than the local name verbatim. In principle, name:latin could be used for this purpose, but there are some problems with that automated approach: onthegomap/planetiler#86.

In the absence of a reliable source of romanizations, we’re left to display names in arbitrary writing systems, which will inevitably run into font issues along the lines of #393.