In the Mapping section, we define the mappings for our T2type architectures:

"Mappings" : {
  "T2type" : {
    "t2.micro" : { "Arch" : "HVM64" },
    "t2.small" : { "Arch" : "HVM64" },
    "t2.medium" : { "Arch" : "HVM64" },
    "t2.large" : { "Arch" : "HVM64" }
 },

The "RegionID" mapping helps the template determine the correct AMI ID to use when starting the EC2 instance. The AMI IDs are region-dependent, so this mapping has a separate AMI ID for every available region:

"RegionID" : {
   "us-east-1" : {"HVM64" : "ami-0ff8a91507f77f867", "HVMG2" : "ami-0a584ac55a7631c0c"},
   "us-west-2" : {"HVM64" : "ami-a0cfeed8", "HVMG2" : "ami-0e09505bc235aa82d"},
   "us-west-1" : {"HVM64" : "ami-0bdb828fd58c52235", "HVMG2" : "ami-066ee5fd4a9ef77f1"},
   "us-east-2" : {"HVM64" : "ami-0b59bfac6be064b78", "HVMG2" : "NOT_SUPPORTED"}
 }

},