Example AWS CloudFormation template which prevents deploying in an unsupported region

cloudformation-region-constraint.yml

AWSTemplateFormatVersion: 2010-09-09
Description: Example of a region constraint
Mappings:
  TheRegionYouAreDeployingIn:
    us-west-2:
      IsNotSupportedPleaseUseADifferentRegion: True
    us-west-1:
      IsNotSupportedPleaseUseADifferentRegion: True
Conditions:
  RunningInAllowedRegion: !Equals [ !FindInMap [ TheRegionYouAreDeployingIn, !Ref 'AWS::Region', IsNotSupportedPleaseUseADifferentRegion ] , True ]
Resources:
  TestTopic:
    Type: AWS::SNS::Topic
    Properties:
      DisplayName: A test sns topic
      TopicName: TestSNSTopic

resulting-error-message.txt

Template error: Unable to get mapping for TheRegionYouAreDeployingIn::us-east-1::IsNotSupportedPleaseUseADifferentRegion