It is hard to predict what would happen if congressional districting were to be redrawn in strict geographic fashion. Whether done by a political process in state legislatures or by simply geographic mapping, the key issue is that district lines be assessed regularly for their fairness.
The other respondent proposed that a geographic mapping of all districts would be more "free and honest." However, districts dominated by one party's power or the others could also take place under a geographic system. Purely geographic boundary lines could yield a greater percentage of districts that were dominated by a particular party, where those geographic areas might tend to be mostly conservative or mostly liberal. Or, over time, the demographic makeup of those geographic areas will change and the original fairness of the process would no longer be valid.
The fact that district lines must be adjusted from time to time is because, without regular review, voting districts can become entrenched and stifle competition. The landmark case regarding voting district lines was Baker v. Carr (1962), which pertained to voting districts in Tennessee. The plaintiff, Charles Baker, argued that voting districts, which had not been redrawn since 1901, heavily favored rural locations over urban centers which had grown significantly since then. Joe Carr was Secretary of State for Tennessee at the time, so was named in the case in regard to voting district lines as drawn by the state legislature. The Supreme Court ruled that voting districts were not merely a political matter to be decided by legislatures, but that they were subject to review by federal courts to determine their fairness.
So perhaps it's not an issue of whether a political process or a strictly geographic mapping process is used. The bottom line is that district lines be assessed regularly for their fairness. The matter of redrawing district lines has come up in court cases again recently as some state legislatures, when dominated by one political party, have gerrymandered district lines to try to maintain continued prominence for their party. That sort of political process is inappropriate. If strictly geographic mapping yielded similar non-competitive results, that would be a form of unfairness also.
