Follow these steps to launch an EC2 instance with an AMI ID that matches your region:

1. Go to the CloudFormation console, and click Create stack.
2. Save the following code to a file on your filesystem:

AWSTemplateFormatVersion: "2010-09-09" 
Description: Demonstrate CloudFormation Mappings
Parameters:
  OperatingSystem: 
    Description: The operating system to run for the instance
    Type: String 
    Default: Linux 
    AllowedValues: 
      - Linux 
      - Windows 
    ConstraintDescription: Must be Linux or Windows
Mappings: 
  RegionMap: 
    us-east-1: 
      Linux: ami-035be7bafff33b6b6
      Windows: ami-0df43b4f8a07c7c14
    us-west-1: 
      Linux: ami-0799ad445b5727125 
      Windows: ami-06b499097655a3ab5
Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: 
        !FindInMap 
          - RegionMap
          - !Ref "AWS::Region"
          - !Ref OperatingSystem 
      InstanceType: t2.micro

3. Select Upload a template to Amazon S3, and choose the file that you just created. Click Next, and give the stack a name. 
4. Click Next, and then Next on the following screen.
5. Click Create.
6. Go to the EC2 dashboard to confirm the creation of the EC2 instance with the correct AMI.
7. Delete the stack.