Admin and water area issues on map display - Australia

[blatchfo]

Description

I went to zoom into Sydney, Australia earlier today and weirdly at quite a low zoom level, Sydney harbour appears to be missing the water area. When you zoom in much closer it does appear, however, the earlier zoom levels are not good. Also, the first AA you see is the council boundaries which feels odd for a map of AUS. Can we make the water area of the harbour appear at higher zoom levels and configure the admin structure to show localities before council areas.

What browser are you seeing the problem on? What version are you running?

Chrome

The OS you're using

Windows

Steps to reproduce

zoom to sydney cbd at various levels to see the issues reported.

GERS ID of the entity in question (if applicable)

No response

The browser URL at the time you encountered the bug

https://explore.overturemaps.org/?mode=explore#11.91/-33.88976/151.22853

[lowlydba]

There is a note on the Sydney Harbor from OSM:

source_tags: | note: this is for the water, not an admin boundary. It uses admin boundaries for simplicity ... if you want to map the water separate from admin boundaries

I am guessing that is the cause of the display issue. What I am less sure about is if we should accommodate that use of admin boundaries for water in Explore Site, or if we prefer for OSM data to be modified accordingly.

Brandon Liu (@bdon) for thoughts

[bdon]

Currently the water polygon is completely missing from the tiles at low zooms:

https://pmtiles.io/#url=https%3A%2F%2Ftiles.overturemaps.org%2F2026-04-15.0%2Fbase.pmtiles&map=11.69/-33.8455/151.2416

[bdon]

We are not correctly lifting subtype=water to a higher zoom level, we are doing it for class=river which is why the polygon to the left looks correct:

https://docs.overturemaps.org/schema/reference/base/types/water_subtype/

We need to:

• likely change the choice of zoom level from using overture schema class to subtype to be broader
• add a rule for subtype=water
• identify other likely missing features based on subtypes without rules

This won't get updated on the explore site until the new tiling code is part of the release process, likely for the May release next month.

[bdon]

create or replace view water as select * from read_parquet('theme=base/type=water/*');
select subtype, count(*) from water group by subtype order by count(*) desc;
┌────────────┬──────────────┐
│  subtype   │ count_star() │
│  varchar   │    int64     │
├────────────┼──────────────┤
│ stream     │     28869175 │
│ water      │     17499776 │
│ canal      │      7533007 │
│ pond       │      3137795 │
│ human_made │      2841906 │
│ river      │      2482410 │
│ reservoir  │      1080324 │
│ lake       │       643815 │
│ spring     │       284470 │
│ physical   │       246322 │
│ ocean      │        53310 │
│ wastewater │         5175 │
└────────────┴──────────────┘

water is the 2nd most common subtype, so it may bloat the tiles to include these at zoom >= 9

[bdon]

Identifying which subtype features have the largest visual impact:

SELECT
           subtype,
           names->'primary',
           sources->0->'record_id',
           ST_Area(ST_Transform(geometry, 'EPSG:4326', 'EPSG:3857')) AS area
         FROM water
         QUALIFY ROW_NUMBER() OVER (
           PARTITION BY subtype
           ORDER BY ST_Area(ST_Transform(geometry, 'EPSG:4326', 'EPSG:3857')) DESC
         ) = 1;
┌────────────┬──────────────────────────────────────────────────────────────────────────────────────────────┬─────────────────────────────────┬────────────────────┐
│  subtype   │                                    ("names" -> 'primary')                                    │ ((sources -> 0) -> 'record_id') │        area        │
│  varchar   │                                             json                                             │              json               │       double       │
├────────────┼──────────────────────────────────────────────────────────────────────────────────────────────┼─────────────────────────────────┼────────────────────┤
│ ocean      │ NULL                                                                                         │ null                            │ 26340189827713.117 │
│ canal      │ NULL                                                                                         │ "r10334380@4"                   │ 60150319.102493316 │
│ river      │ "Río de la Plata"                                                                            │ "r3474227@233"                  │  45310398834.39087 │
│ human_made │ "Salinas Guerrero Negro"                                                                     │ "r16265322@3"                   │  321799150.2854536 │
│ stream     │ NULL                                                                                         │ "r8062731@25"                   │  183702078.9898424 │
│ wastewater │ NULL                                                                                         │ "w340558066@7"                  │  5862828.466465488 │
│ pond       │ NULL                                                                                         │ "w366357264@2"                  │  590819120.9099965 │
│ spring     │ "Давыдов ключ"                                                                               │ "w1096701607@1"                 │ 64374641.441837884 │
│ reservoir  │ "Хантайское водохранилище"                                                                   │ "r184889@47"                    │  15998058374.97723 │
│ water      │ "Lake Hazen"                                                                                 │ "r18767527@2"                   │ 26980505922.239685 │
│ lake       │ "Каспий теңізі - Hazar deňizi - دریای خزر - Xəzər dənizi - Каспийское море - دریای مازندران" │ "r3987743@330"                  │  668091801255.6746 │
│ physical   │ "Баренцево море"                                                                             │ "r9382300@213"                  │ 23224551991710.504 │
└────────────┴──────────────────────────────────────────────────────────────────────────────────────────────┴─────────────────────────────────┴────────────────────┘
  12 rows                                                                                                                                                4 columns

[bdon]

Also, the first AA you see is the council boundaries which feels odd for a map of AUS. Can we make the water area of the harbour appear at higher zoom levels and configure the admin structure to show localities before council areas.

This is going to be difficult without a cartography property for localities, because otherwise the smaller localities are going to knock out the expected ones - we want to see Sydney before smaller towns around it. We are already using population as a coarse signal but this is often absent or leads to unexpected results (population of metro area vs. administrative division)