.MSD File Extension
File TypeMap Service Definition File
This file is saved in a binary format, which requires a specific program to read its contents.
What is an MSD file?
Published map file created by ArcGIS Desktop, a software suite used to create maps and process geospatial data; contains a map that has been published from an .MXD map document; created for ArcGIS Server, which hosts the map for real-time viewing over a network.