Files with blockmap extension can be found within Windows app installer packages. Contains list of app files, indexes and cryptographic hashes for each block of data.
BLOCKMAP file extension - App package block map
What is blockmap file? How to open blockmap files?
File type specification:
File extension blockmap is best known for one of te XML files that can be found in Windows installer app packages.
According to Microsoft, the package block map file is an XML document that contains a list of the app’s files along with indexes and cryptographic hashes for each block of data that is stored in the package.