It is an analogy. North Carolina is to South Carolina as North Dakota is to South Dakota.
North Dakota is north of South Dakota.
The US state of North Dakota is north of South Dakota.
North Dakota is up by the border of Canada, Wyoming is just next to South Dakota.
North Dakota South Dakota North Carolina South Carolina
The state of North Dakota is north (or above) the state of South Dakota.
Saskatchewan and Manitoba, Canada are to the north of North Dakota and North Dakota is to the north of South Dakota.
The state of South Dakota is south of North Dakota.
North Dakota is bordered by South Dakota to the south.
South Dakota is further north than North Carolina.
In general, the directions north, south, east, and west are not capitalized unless they are part of a proper noun or at the beginning of a sentence.
North Carolina is to South Carolina as is to North Dakotais to South Dakota.