City data includes a count of cases per 10,000 residents in each of its 13 neighborhoods.

Cambridge began reporting Covid-19 cases in each of the city’s 13 neighborhoods Tuesday, new data that could make it easier for public health analysts to pinpoint disparities in the impact of the virus on the city’s population. But many people who have tested positive – 81 as of Friday – are not included.

The reason: Their addresses as reported to the Cambridge Public Health Department were misspelled, incomplete or had other problems, and a software program the city uses to match addresses to neighborhoods could not match theirs. The entire address “needs to match to a real Cambridge address,” department spokeswoman Susan Feinberg said, quoting the agency’s epidemiologists.

Boston University assistant professor of epidemiology Eleanor J. Murray said the omitted cases shouldn’t matter as long as the fact that the addresses are missing “has nothing to do with the neighborhood a person is in.” For example, she said, hypothetically people in certain neighborhoods “may be more distrustful of giving the government their address.”

Epidemiologists need to “figure out why that data is missing,” she said. Murray also said there are probably many more cases missing because of inadequate testing for the virus.

Feinerg said: “There is no easy way to determine if the missing addresses are disproportionately occurring among a specific group or groups of residents.  We are sharing the data that we have in the form that we have it, we are not conducting a formal epidemiologic study.”

The city’s new neighborhood map, published daily, includes the number of cases and cases per 10,000 residents – the rate – by neighborhood; Chief Public Health Officer Claude Jacob has said the rate is the best tool for comparison. Infections among nursing home and assisted living residents aren’t included. Looking at neighborhoods allows the health department to use a wealth of demographic information on neighborhoods that was prepared by the Community Development Department.

For instance, The Port had the highest number of Covid-19 cases per 10,000 residents as of Friday – 89 – and also has considerable density at 36.9 persons per acre, the second-highest percentage of black residents, 20.4, and a relatively high proportion of people living below poverty, 16.8, all measures of vulnerability to infection.

But those factors aren’t always dispositive. Riverside, Cambridgeport and Mid-Cambridge have more people per acre, and North Cambridge has a higher percentage of black residents and close to the same percentage of residents below the poverty line, all with lower coronavirus case rates. East Cambridge was a close second to The Port with an infection rate at 87 cases per 10,000 residents; black residents make up 9.6 percent of its population; and the poverty level is 16.3 percent.

And Cambridge Highlands, the sparsely populated area near Fresh Pond, has only 11 cases but an infection rate of 83 per 10,000 residents because of its low population. The neighborhood has a low poverty rate and black population.

The health department continues to publish case rates by ZIP code. Only 26 cases were missing from those figures on Friday – because, the health department epidemiologists quoted by Feinberg explained, most cases do have a ZIP code, even if they have no address. The cases come to the city from the state Department of Public Health tracking system called Maven.

ZIP codes may include part of several neighborhoods. The East Cambridge code, 02141, continues to have the highest Covid-19 infection rate at 83 cases per 10,000 population; it also includes much of Wellington-Harrington. ZIP code 02139 covers Cambridgeport and The Port.