Withheld estimates

A blank area is not a zero

The American Community Survey is a sample of households. Where the sample behind an estimate is too small to publish, the Census Bureau withholds the number, and on a map the withheld estimate arrives as a blank area. A blank area is easily read as a zero, although it says nothing about whether the value is low.

Finer levels have fewer households behind each estimate, so the level that resolves the most detail also has the most blanks. The sources page lists every dataset and boundary year behind the figures on this site.

Three kinds of blank

In New York City, median household income is blank for 132 of 2,324 census tracts: 81 have no residents, 12 have fewer than 50, and 39 have residents and a withheld estimate. The city maps on this site keep the three apart.

No residents

The population is zero: a park, an airport, a cemetery or open water. No household lives there to have a median income, and the map is right to be empty.

Fewer than 50 residents

People live here and no estimate is published, which is expected with so few households. The threshold of 50 is this site’s choice, and the maps state it.

Withheld

People live here and the Census Bureau published no estimate, because too few sampled households answered to support one. This is the case a blank area hides.

A fourth blank, an area whose boundary has no row in the estimates at all, is the subject of boundaries from the wrong decade.

Finer levels withhold more

A block group sits inside a tract and has fewer sampled households behind each estimate, so its margin of error is wider and the Bureau withholds it more often. Public Use Microdata Areas (PUMAs) hold at least 100,000 people each, and none of their estimates of these four measures is withheld in New York City, Los Angeles County or Cook County.

Which measure is withheld most often at block group depends on the place: median home value in New York City (2,188 of 6,804, 32.2%), rent burden in Los Angeles County (763 of 6,588, 11.6%) and rent burden in Cook County (1,037 of 4,001, 25.9%). Median home value describes owner-occupied homes only and rent burden, the median share of income that renter households pay in rent, describes renters only, so each is withheld where the sample holds few households of that kind.

Bachelor’s degree share is computed by this site from published counts of adults by education, which the Bureau does not withhold, so it is blank only where no adults aged 25 or older live.

How the city maps show a blank

Each city map states its withheld count under the legend, in areas and as a share. Areas with no residents or fewer than 50 share a quiet fill, withheld areas take a separate grey, and neither matches the page background, so a blank area reads as a blank rather than as canvas. No withheld value is drawn as a zero or filled in from its neighbours.

Margins of error are not drawn yet

A published block-group estimate can carry a margin of error close to the size of the estimate itself, and the map draws it like any other. The planned remedy is a map form that visibly withdraws areas whose margin crosses a threshold, so a reader can see which estimates are precise enough to compare. It is described in the component catalog and not built, because the estimates files on this site carry no margins of error.