The Commonwealth of Massachusetts provides a state-wide Geographic Information System, including Oliver, their online data viewer.
Embedded Maps and Apps
Concord GIS develops webmaps to embed in other pages on the Town's website. Here's an example:
Assessor Tax Map - Search for a Concord address in upper right to zoom to a parcel. Click inside the parcel polygon to link to the Property Record Card for that property. View a larger version of the map by clicking "View larger map" at lower left.