Use Case: Provide alternative map layers which the user can select

[NickFitz]

This issue is for discussion of the use case "Provide alternative map layers which the user can select".

[prushforth]

MapML proposal

[NickFitz]

This idea originally arose from considerations such as a visually impaired user wishing to select a high contrast map, but it seems that this is more appropriate to issue #82, as the style in question would be an attribute of the selected layer, assuming "layer" is the most suitable term.

[AmeliaBR]

At the use case level, we can talk about this as a "map" feature: the user wants to select dark mode or high contrast mode, or so on. On a capability level, this would probably need to be implemented for each layer independently.

[AmeliaBR]

After the merger of use cases, this issue/use case is specifically about selecting map styles that involve switching map sources: e.g., switching from street map to satellite photos, or from dark mode to light mode or high contrast tiles.

It's listed as an authoring use case, since the author needs to provide the different map options (if it's not part of the default map for a given framework).

[shepazu]

Perhaps we should clarify in the wording that this is about changing the basemap layer, as opposed to selecting other overlay layers.

[shepazu]

Is it in scope for this use case that you might select a basemap layer from different providers (e.g. change from OSM to Google Maps)?

[prushforth]

Is it in scope for this use case that you might select a basemap layer from different providers (e.g. change from OSM to Google Maps)?

In the MapML proposal, based on / required by the WMS concept of "named styles", we give the map layer author the ability to provide a <link rel="style" ...>. The token style is a new rel value. A set of such links, provide a set of alternate contents that the map layer author considers to be equivalent content with a different style than the current layer content, which is identified among those alternates with a <link rel="self style"...> link. Because the href of those links can link to any MapML document, not only one produced by a WMS over its named styles, it could be a general mechanism for "switching basemaps", among other things. So for example, you often see "Satellite View" and "Map View" as 'alternate' possibilities for a given map. This feature could do that, but because the interface to the map document is a simple URL, the author is free to designate any other service (Google, MapBox, OpenStreetMap etc.) as being an alternate 'style' for the current one.

[caseymm]

I'd like second @shepazu's comment:

Perhaps we should clarify in the wording that this is about changing the basemap layer, as opposed to selecting other overlay layers.

When I originally looked at this item in the spec I expected this to be related to layers that one might want to add on top of the basemap, not changing the basemap layer itself. The image included in this section of the spec showed me that my original understand was likely wrong, and that this item is actually focused on adding options for basemap layers, but it wasn't clear to me at first.

[prushforth]

@caseymm I agree there are several use cases mixed in here.

The first/primordial one is the over here very concept of "layer" itself. Maps have layers. Users need to turn layers on and off. Users may need to add layers to a map. Layers may not be overlay-compatible with one another (opaque), so the user needs to be able to adjust opacity. And so on.

The next use case, this one (I think), highlighted by this example, is the capability of changing / swapping one layer for another by presenting them as mutually exclusive options selectable by the user. Per the Google Maps embed example, these are often held out as different "styles" of the same reality (e.g. satellite vs map view).

The final use case that is alluded to here would be (perhaps) automatic selection of a layer source by the user agent, based on a user preference such as light / dark mode. That issue is over here: #43

Perhaps we should clarify in the wording that this is about changing the basemap layer, as opposed to selecting other overlay layers.

Please suggest some wording!