In so many words, the folks in Phillips Ranch and Westmont are being overrepresented, while people in North Pomona and Northeast Pomona are getting less representation. The "ideal" district population (population of city divided by number of districts) is 24,843, and District 5, where Phillips Ranch and Westmont are, has only 20,354 people, while North Pomona has 27,115 people.
In typical bureaucrat form, City staff gives the Council an option of maintaining the existing districts, using the excuse that because of foreclosures in District 5, "changing district boundaries at this time would likely create future inequality". However, this reason is hollow since the number of foreclosures in District 5 are not likely to be worse than the rest of Pomona. A 18.07% deviation from the ideal population is very high and would violate the U.S. Constitution, which calls for "one person, one vote", as determined in Reynolds vs. Sims. Keeping existing districts would invite a legal challenge from those in North and Northeast Pomona who feel underrepresented. Such legal costs would likely dwarf the several thousand necessary to draw properly apportioned districts.
In addition, since District 5 is considered more affluent and less Hispanic than the other districts (demographically speaking), maintaining the existing district lines could cause problems with the Voting Rights Act, which states that minority groups should have an opportunity to vote for candidates of their own choosing. Incidentally, Phillips Ranch also has a higher than average Asian American population, and it could be argued that by diluting the district, it lessens the ability for Asians to elect a candidate of their own choosing. The City went to district elections partly because of Voting Rights Act concerns. Other cities have had malapportioned districts as well for some time (Bradbury is a recent example) but it is less of an issue since there are not significant numbers of minority groups that are protected by the Voting Rights Act. This will also affect the ballot initiative by Vernon Price which is proposing to return to at-large elections of candidates who live in individual districts, but may require Voting Rights Act analysis if passed to ensure that Caucasians, Asians, and African Americans have the opportunity to select candidates of their choosing.
However, the current districts correspond with major arterials and easily identifiable neighborhoods. One common complaint is that the current districts split up the Downtown area, but some argue that splitting up Downtown is fine since more councilmembers have a stake in Downtown. Also, District 6 is compact in that it includes all residents north of the 10 freeway. Any redistricting would likely eliminate that - the most obvious way to redistrict District 6 without breaking up neighborhoods is to move the Val Verde neighborhood into District 1 (as part of a compound move that shifts all of Pomona west of the 71 freeway into District 5), but Stephen Atchley lives in Val Verde. It is very unlikely that any redistricting would pass that ousts any sitting councilmember from their seat.
Another possible redistricting could include shifting District 5 north to the Kellogg Park neighborhood and the area around Ganesha High School (Valwood Estates), District 1 north to cover Wilton Heights (while keeping the Fairplex in District 6, allowing for Val Verde and Stephen Atchley to continue to represent that district), and District 3 to come up along Indian Hill to cover the eastern flank of the city. Either way, the citizen voting age population by ethnic group will need to be checked to ensure that minority voting power is not substantially modified.
See the City staff report here. And if you want to do your own redistricting, Dave's Redistricting Application is an example of a basic web-based redistricting application that includes Census block groups. With the City's legal bills mounting with the Avila lawsuit, trash station theater, and other issues, I would doubt that the City Attorney would recommend to invite more legal troubles. But you never know.