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Subject (Region)
- District of Columbia33
- Maryland10
- Ohio River6
- Chesapeake and Ohio Canal (District of Columbia/Maryland/West Virginia)5
- Germany (to 1949; 1990- )5
- Louisville and Portland Canal (Kentucky)5
- Pennsylvania5
- New York4
- Potomac River4
- Cincinnati, Ohio3
- France3
- Great Britain3
- Indiana3
- Kansas3
- New York, New York3
- Nicaragua3
- Nicaragua Canal (Nicaragua)3
- Ohio3
- Virginia3
- West Virginia3