How a county can be mostly water

The Census geography glossary describes water area as including inland, coastal, Great Lakes, and territorial sea water. Those categories explain why the number can be much larger than the lakes you recognize on a county’s land map. The Gazetteer supplies a combined water measurement; our download does not break a county’s total into those four categories. Read the Census area definitions.

That limitation matters when writing an explanation. A high total tells you how the geography is measured, but it does not identify which individual lake, inlet, or offshore segment contributes each square mile. For that, inspect appropriate detailed geography and water features. Do not infer a shoreline length, drinking-water supply, or proportion of wetlands from the single water-area field.

Lake and Peninsula Borough, Alaska has the largest original water-area measurement in this release. It contains 63.1 times Culebra’s published water square miles, yet its water share is 29.3%, below Culebra’s 93.1%.

There is no contradiction. Water share divides water by land plus water. A jurisdiction with a very small land component can have an enormous percentage without an enormous absolute water area. Before calling a place the “wettest county,” decide which of those claims you mean. Neither measurement describes rainfall. For a table about water extent, sort water area; for a table about the composition of each geography, sort water share.

Wexford has more land than Keweenaw in the 2026 figures. Once water is included, Keweenaw’s 5,966.3 square miles of total area substantially exceed Wexford’s 575.4. A reader given only “county size” could reasonably misunderstand which comparison was being made.

Open the side-by-side comparison and examine all three rows. The land bar answers the land question. The water and total rows explain the reversal. This is a useful pattern for reporting other county comparisons: show the component that changes the conclusion instead of presenting a different rank as an unexplained curiosity.

For Culebra, the calculation is 157.185 ÷ (11.647 + 157.185) × 100. That yields approximately 93.1% water. The denominator must include both components. Dividing water by land instead produces a water-to-land ratio, which can exceed 100% and answers a different question.

In a spreadsheet, divide waterSqMi by totalSqMi and format the result as a percentage. Do not also multiply by 100 when using percentage formatting, or the displayed result will be one hundred times too large. Our ranking uses the published square-mile fields. A calculation using the more precise square-meter fields may differ in the final digits because the source’s square-mile values are rounded.

The site’s county outlines are generalized cartographic shapes, displayed as a single fill. They are not land-versus-water classification maps. The Census also notes that simplified cartographic boundaries can omit offshore areas and small features. You cannot audit the Gazetteer water total by counting colored pixels in that illustration. The boundary-file documentation explains the intended use.

Instead, audit the table: match the GEOID, compare the original water field, and keep the release year. If the research question requires the exact location of water, use a suitable detailed geographic source and document its date and categories separately. A small reference map and a numerical inventory serve different purposes; neither becomes more reliable by pretending they are interchangeable.

A high water share supports a narrow and useful statement: much of the geography’s measured total is water under the Census definition. It does not establish flood probability, recreational access, navigability, or ownership. It also does not say that a certain percentage of residents live near water. Those claims would need additional datasets and a more specific spatial question.

For classroom or editorial use, pair the water-share ranking with the total-area ranking, then choose two examples that switch order. State the formulas and let readers reproduce the comparison. That provides a stronger explanation than a list of surprising percentages because it shows exactly how a definition can change the story.