An orthomosaic is a collection aerial photograph geometrically corrected (“orthorectified”) where the scale is uniform. Its the mosaic of all aerial photos captured during the flight run corrected for its distortion.
Digital Elevation Model (DEM) - A digital elevation model is a digital model or 3D representation of aterrain's surface created from terrain elevation data.
Digital terrain models (DTM) - These are representations of land surface point elevations. They are usedas input for the generation of surface models and contours or theorthorectification process of aerial photography.
Digitial Surface Model (DSM) - A DSM is an elevation model that includes the tops of buildings, trees,powerlines, and any other objects. Commonly this is seen as a canopymodel and only 'sees' ground where there is nothing else overtop of it.
Basemaps provide a visualization framework for all GIS server applications.