ZIP codes in a drawn area

Worked example: the Salt Lake Valley

The tool opens with a six-corner shape around the Salt Lake Valley, from the airport in the north to the Point of the Mountain in the south, with the Wasatch foothills on the east side. The shape covers about 329 square miles. Inside it sit the internal points of 33 ZCTAs, from 84009 to 84180, with a combined land area of about 248 square miles.

The list shows how ZCTAs behave at the edge. Herriman city is inside the shape, but ZCTA 84096, which carries the Herriman name, is not: its internal point sits at 40.487° N, 112.100° W, west of the shape's southwest edge, because most of that ZCTA's land reaches into the Oquirrh foothills. Magna's 84044 is left out for the same reason. Move the west corners a few miles and both appear.

At the other extreme, four downtown Salt Lake City codes (84114, 84138, 84150, and 84180) each cover less than a tenth of a square mile. They are real ZCTAs, so a mailing or targeting list built from this shape includes them.

How to use it

1. The map opens on a sample shape around the Salt Lake Valley. Press Clear to start your own, then pan and zoom to your area.
2. Click the map to add corners in order around the edge, or type a place or coordinates in Add a corner. After the third corner the shape closes and fills.
3. Press Undo to remove the last corner. The count next to the buttons shows how many corners the shape has.
4. Read the card: the number of ZCTAs inside, their combined land area, the drawn area, and the corner count. Orange dots mark each ZCTA's internal point.
5. Press Copy as list for comma-separated codes or Download CSV for codes, coordinates, and land area. The table below lists every code. Copy the page address to share the shape.

Why draw a shape instead of a circle

Service areas, sales territories, and delivery zones rarely look like circles. A valley is bounded by mountains, a metro area by a river or a state line, a franchise territory by highways. A radius either spills past those edges or misses parts of the area. A drawn shape follows the boundary you actually care about.

The result is a plain list of five-digit codes, which is what most CRM filters, ad platforms, and shipping tables expect. For a quick circle, the ZIP codes within a radius tool is faster.

ZIP codes and ZCTAs

Postal ZIP codes are delivery routes, not areas with fixed borders. The Census Bureau builds ZIP Code Tabulation Areas by assigning census blocks to the ZIP code most common among their addresses. The 2024 Gazetteer lists 33,791 ZCTAs, each with one internal point and a land area, and that is the file this tool searches.

Most ZCTA codes match a ZIP code you would write on an envelope. ZIP codes used only for PO boxes or a single large mail recipient often have no ZCTA, so they never appear in the list.

How a ZCTA is counted

Each ZCTA is one point. It is listed when that point is inside your shape and left out otherwise, with no partial overlaps. A large rural ZCTA that crosses your edge counts only if its point is on your side. The land area column is the whole ZCTA's land from the Gazetteer, not the part inside the shape, which is why the total can be larger or smaller than the drawn area.

The test treats longitude and latitude as flat coordinates, which matches how the shape looks on the map. Each edge takes the short way round, so a shape across the 180th meridian near the Aleutians works too. If two edges cross, the outline has no single inside, so the tool shows a notice and holds back the list until you move a corner. Keep corners in order around the edge to avoid that.

Saving and sharing a shape

Every corner is written to the page address as you draw, rounded to five decimal places, about one meter. Copy the address bar to save the shape or send it to someone; opening the link redraws the same corners and recomputes the list from the current files. Clear removes the shape, and Undo removes the last corner. A cleared map or a shape with only one or two corners is saved too, and a shape can have up to 200 corners.