If there is an urban undercount, I suspect it is among the most affluent, not the underclass. In the poorer neighborhoods the message that we're from the government and we're here to help you get more money has been widely communicated.  In highly affluent areas responding to the census taker is just another competing claim on very valuable time by those who value their privacy.

I base this on a conversation I had in 2000 with an insurance executive at a political event in Chicago. Let go after a merger had created staff redundancies, she had taken a temporary position organizing the 2000 census.  She told me that while the media stories about any undercounting tended to emphasize those in Chicago's poor neighborhoods, the largest problem she had was trying to get an accurate count along the affluent north lakefront. Employees of social service agencies and ministers at local churches did a fine job of letting Chicago's poor people know how important it was to return the census questionnaires. Initial response rates from those neighborhoods were encouraging. Those same questionnaires seemed to be getting lost among the masses of junk mail solicitations people who live in affluent zip codes always receive.  Thus the initial response rates from neighborhoods such as the one we were in, Lincoln Park, were lower while the security systems of the affluent made follow up much more difficult.

Both veterans of local political campaigns, we talked about how her problems with the census correlated with problems encountered both getting affluent, career driven residents with few ties to the neighborhood to register to vote in local elections (think Caroline Kennedy's voting record) and with thwarting various security systems to deliver candidate information to each door in a precinct.   Over the years my acquaintance and I had beaten a few of those systems. Someone in the campaign would find a friend who'd buzz us in, or sometimes we'd just stand by the door and wait for the next person to exit. That worked because we looked like we lived in that building.  Few of her census workers looked like they might live in a million dollar apartment overlooking Lake Shore Drive and they had to make personal contact with those who had not responded to the mailings, not just shove a flyer under each door.  My acquaintance noted that those apartment buildings and gated townhouse complexes that had no on-site manager where next to impossible for her staff to access.  Where there was a building manager on site, the task of the census taker wasn't all that much easier. She was irked at how many building managers were reluctant to cooperate until she told them the law was on her side.  Even then, it often wasn't a pleasant task. People who pay dearly for security cameras, key cards, doormen and other types of gate keeping weren't always civil when contacted in person by the census taker.