A map layer is an object that contains information on the location of objects that are to be shown on a map, where within that object's structure to draw the latitude and longitude from and what colour to display these objects as.
Multiple map layers can be displayed on a single map, so multiple sets of objects can be displayed on same map, each set being shown as a seperate colour and seperate layer within the legend (see Google Maps Atom help).
It also contains the "Tag Template" for the map item. This is basically an html area that has access to all the fields from the object type you are displaying, allowing you to "mail merge" content into the tag bubble that pops up when you click on a location pointer.
For example, the image below shows a map with three layers, and a simple tag popup.
This is very similar to content repeaters.
You select a Root object (an object within the system from which to start repeating your objects from, then choose a data source (Children, Parents, Associated Objects, etc). Choose an object type to display from the dropdown list, and a published status (if relevant, otherwise leave it as "Ignore")
The search query allows you to limit your information down (for example if you have a field on the object type that represents private you could choose to exclude said items from your results).
Latitude and Longitude are dropdowns for you to choose which fields in the object represent these (in case you are using a custom object type that does not inherit an address).
Marker colour is the chosen colour of your location markers.
Once you have selected all of these, if you have a Google Map atom on your website with a Root of a folder that contains this Map Layer your items will be displayed. No information will appear in the Tag as you have not configured it.
Tag configuration is identical to using Content Repeaters (see Supporting Resources)
Root ObjectId An object that is the starting point for finding the objects you wish to appear on the map. It must be associated to or recursively associated to the objects to be repeated.
Data Source Type
Children One of the two most common associations, a child object of the selected Root Object Example: regional offices of a national company
Parents The other most common association, a parent of the selected Root Object Example: regional offices managed by a single staff member (where the member is a "child" of each office)
Single Object A single object. In this case the Root Object. Example: The Head Office of the national company.
Associated Objects Similar to children, however allows you to use any other association type Example: Organisations that have purchased items from the national company
Associations Recursive As with associated objects it allows you to see associations of the type selected, however they do not have to be direct associations. Example: Organisations whose details are stored within groups within the national organisation (they are one assocation removed)
Object Type The type of object that you intend to display on the map (organisations, people, etc)
Association Type (only shown if the Data Source Type is "Associated Objects" or "Associations Recursive" Any allowed association type between the Root Object and the selected Object Type
Published Status Some objects can be published (see News Articles) and if they can this dropdown allows you to display them or not based on their published status
Search Query This will open a window that allows you to visually generate a set of rules based on the properties of the selected Object Type and their allowed values. ie. Organisations created after 5th April 20xx
Latitute Field This is the property within the selected Object Type that represents the Latitute component for the map. If the Object Type is / inherits an Address then this is calculated automatically from the entered address details
Longitude Field This is the property within the selected Object Type that represents the Longitude component for the map. If the Object Type is / inherits an Address then this is calculated automatically from the entered address details
Marker Colour A colour picker that allows you to choose the colour of the location markers for objects rendered by this Map Layer
HTML Tag Template Editor This is a HTML editor that allows you to mail merge content into the tag bubble that pops up when you click on the marker. This merges properties in an identical manner to the Content Repeater (see Supporting Resource)