prushforth
commented
5 years ago URL templates are more or less the standard way of accessing map content. What is usually not standard is the way that template variable values are supplied to the template, as far as I know. An example is the OpenStreetMap URL template that is featured in many Leaflet (and perhaps OpenLayers, though they seem to hide it a bit more) example maps: https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png. Where are the names "s", "z" "x" and "y" defined? In an HTML form, (if forms were capable of respecting such templates -they aren't, but it is as close an example as I can come up with), the form inputs would define the both the names and values of the variables. Its this step that seems to me to be missing from all the example Web mapping services and libraries being examined. Moreover, its the step that sets the Web apart from the tightly coupled designs of Web mapping.
So, how does this relate to requirements and use cases for Web mapping? In my opinion, the requirements aren't only dictated by how it is currently done, they should also be drawn from how it could or even should be done in a Web browser.
It's this decoupling that drives the design of MapML. Its true also of HTML, but it is so expected there that its hardly worth mentioning, whereas the opposite is true of Web mapping solutions.
I came across the term URL recipe in the document, and I wanted to make a point that open source libraries typically allow you to provide a URL template to access tile content, while service definitions like WMS require you to follow a recipe to create a valid URL to a map or image. Finally these have to be considered distinct from a standard URL because they both require additional preprocessing steps in order to access content, and what's more the content being accessed has a particular semantic in context.
FWIW!