After a few days with this plug-in, here is my take, which may help others get started.
Leaflet Maps Marker is a brilliant plug-in for WordPress which lets you embed scrollable and zoomable maps into your WordPress pages. Nearly all the configuration is done from the WordPress back-end and for simple tasks the learning curve is very short. If you just want a map with a few markers on it with pre-selected icons (and there are lots to chose from), you will be up and running in no time. For more sophisticated maps, the way the layers, customizable base maps, WMS data and “overlays” work take some time to understand but there is lots you can do with these.
A marker is defined within its own map and can be displayed without assigning it to a “layer”. To display multiple markers, you assign them to the same layer and show that layer on your map. Several layers can be added to a “multi-layer”. You can’t have a marker assigned to more than one layer, but you can have a layer on several different multi-layers so it is very flexible. Our site has a map in each section and they share some markers but not others. MapsMarker does this painlessly. You can put anything into a marker’s pop-up and there’s a link to Google’s directions by default!
Base maps can be selected from pre-defined sets: OpenStreetMap, MapQuest, Google, Bing as well as Cloudmade and MapBox. There are also three “custom basemap” settings which you can point to a TMS or WMTS but not, apparently, a WMS server. UK users may regret the apparent lack of support for OSOpenSpace (with its fixed SRS and variable tile size).
WMS data can be added to any map, but they are not user-switchable. The site admin determines whether or not they show on each map. There are 10 configurable settings, each of which could pull multiple layers from its server. The data is displayed in the style(s) determined by the server, which may not be ideal. There is no opacity setting for overlaying filled polygons. Also, you cannot choose which zooms the data is displayed at.
“Overlays” are different. They are user switchable. Site admin determines which overlays are available and at which zooms, (global settings for all maps,) and which are turned on for each map when that map is first loaded. There is also an opacity setting so you can fade out filled polygons to your taste. Overlays use WMTS or TMS servers but not WMS. You can make your own tile sets (with other software) and store them on your own website, so again it’s very flexible. It’s a pity there are only 4 settings provided, and it would be nice if you could choose for each map which of these overlays are available to site users.
Support for vectors (routes and tracks, for example) appears limited, (non-existent?) and there is currently no facility for allowing user input to the map. There is, however, an API which allows remote creation of markers, so user input could probably be programmed using that.