[openstreetmap/openstreetmap-website] Dashboard map under/overzooms map tiles at fractional zoom levels (Issue #6618)

[Minh Nguyễn]

1ec5 left a comment (openstreetmap/openstreetmap-website#6618)

> Processing raster geo-data - both photographic and cartographic - is a tricky field where both theoretical knowledge and practical experience are significant to achieve good quality results.

Indeed, and I’m sorry if my terminology and link-dropping has muddled the conversation. Especially when I work in mobile application development, terms like “scale” are severely overloaded (almost as much as “layer”), so it’s easy to conflate independent variables. In case it isn’t clear, I’m also assuming that any resolution to this issue will involve a tradeoff of some sort.

It’s absolutely true that the OSM Carto style can accommodate different pixel densities (to use a less overloaded term). The limiting factors of course are the tile images that are being produced from that style and what’s displaying them on the client side. Pixel grid alignment is also an issue, one that unfortunately I can’t reproduce as easily because both my devices have 2× HiDPI displays.

What I’d like to get out of this conversation is whether the current main map (or the dashboard map prior to #6504) steers clear of the concern you’ve raised. If so, then “don’t do it” suggests that we could disable incremental zooming whenever a map shows the Standard layer and reenable incremental zooming whenever it shows the Shortbread or MapTiler OMT layer. As Those vector layers’ underlying stylesheets, as MapLibre styles, are ostensibly designed for incremental zooming, though I can’t vouch for the quality.

We would be trading off the user experience. For better or worse, computer users these days are accustomed to smooth interface animations and will be jarred by any discrete transition, no matter the cause. Leaflet mitigates each zoom transition with a linear animation, which the new dashboard map could simulate using a zoom event handler. Ideally this would be supported by a built-in option upstream in MapLibre. Eventually, the main map will need to handle switching from a vector layer to a raster layer by snapping the zoom level at the interface level, so we’d once again need to decide between rounding, flooring, or ceilinging.

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