The OpenLayers core code stores map configurations: maps, styles, layers, and behaviors, and combines them to create maps using the OpenLayers JavaScript library on any Drupal site.
OpenLayers supports a wide range of map types and new types can easily be added as ctools exportables - new layer types are being added all the time. Currently the module supports OpenStreetMap, Google Maps, Yahoo Maps, Bing Maps, TMS, WMS, CloudMade, XYZ map types and the MapBox maps.
OpenLayers supports a wide range projections and new ones can easily be added as ctools exportables. Proj4JS is the JS library who allows to create custom projections, so, the proj4js module is now a dependency.
Map interactions like popups, zoom controls, editing, and fullscreen can be added via the UI and extended by other modules.
OpenLayers UI
This module allows for a user interface to create and store maps which can be used to customize all sorts of things like CCK Formatters to Views Plugins. Maps can be provided by code or stored in the database and integrated with Features.
OpenLayers Views
The Views module is the preferred system of putting an OpenLayers map on a page: two types are provided - OpenLayers Data and OpenLayers Map, so that a single map can contain multiple node types and views.