In the Garden State, redistricting is done by a bipartisan commission. If the commission fails to pass a plan, it then falls to the courts. As such, the current map is the likely starting point for any new map.
Currently, the Democrats hold ten of the twelve seats, but the map actually creates six Democratic districts, one Republican district, and five toss-up districts. At the present time, the overpopulated part of the state is the three districts that contain Newark and the suburbs of New York
City (the Eighth District, the Ninth District, and the Tenth District). the other district that is significantly overpopulated is the Twelfth District in the western part of the state around Princeton. All four of these districts are solidly Democratic. The two most underpopulated parts of the state are the two districts in the southern part of the state — the First (the southwest part of the state around Camden) and the Second (the rest of the south New Jersey). Given the population pattern in the state, all of the lines in the state are going to shift toward New York City.
As in other urbanized states, the Voting Rights Act will be some consideration. There are five minority-majority districts (Sixth, Eight, Ninth, Tenth, and Twelfth) with Hispanics being the largest group in two districts (the Eight — in which they are the majority — and the Ninth) and African Americans being a majority in one district (the Tenth).
The key thing about New Jersey is that the population differences are minor. If you add the fuve southern districts together (First, Second, Third, Fourth, and Sixth), you only have a combined shortfall of around 46,000 persons. So at the northern end of the shift, you are talking about 5-7% of the population of the new district. Even with a 2-1 split in the new voters in the districts, that would only move the needle by about 2%. And given that most of the boundaries of the old districts are already in lean Republican areas, it’s unlikely that any new map would significantly alter the balance.
The current maps split more counties than are needed. By drawing lines that respect county lines (with one exception needed to respect the homes of current representatives), the map would actually be slightly more favorable to the Democrats. (It would require the representatives from the Fifth and Ninth District flipping districts as the Ninth is mostly based in Bergen County which can be a single district, but the representative from the Ninth lives in Passaic County with the representative from the Fifth which is mostly northern New Jersey including much of Passaic County lives in Bergen County, but both districts would be safe Democratic as opposed to the current map that makes the Ninth solidly Democratic and the Fifth a swing district that slightly favors the Republicans.) The redrawn map would have eight safe to solid Democratic districts, one safe Republican district, one lean Republican district (currently represented by a Democrat), and two swing districts (currently split). Both of the swing districts would slightly favor Republicans (by about 2-3% each(. But avoiding split counties does have some impact on minority representation — for example increasing minority influence in the Fifth while reducing it in the Ninth. While the current map makes an 11-1 split possible, it is actually a 6-6 map. But the Republicans have run such poor candidates that the Democrats have been able to win 4 of the 5 districts swing districts even though all slightly favor the Republicans.
In short, the issue in New Jersey is whether to continue drawing the lines in a way that maximizes the number of competitive districts (which is essentially a gerrymander in favor of the Republicans) or to draw lines that recognize the political subdivisions of the state (which would reduce the number of competitive districts with two of the current five swing district becoming lean to safe Democratic districts and one becoming a lean Republican district leaving only two real swing districts).
