The first debate for New York’s 20th Congressional District will take place in Saratoga Springs this Tuesday, four weeks before the March 31st vote. Before the media turn their focus exclusively upon the candidates, their war chests and attack ads, let’s take a moment to contemplate the peculiar 10-county district itself. And — more broadly — the process by which such a tortured political boundary is created.

With $12.5 million in campaign disbursements, the 20th CD became notorious last year as one of the country’s most expensive house races. While it held the number one position in November, by the time the last campaign finance reports were in, it had slipped to second place behind California’s 4th CD, which lumbered in at $16 million plus.

The high cost of the once stable Republican district owes to the perception among state and national GOP leaders that the defeat two years earlier of John Sweeney by Kirsten Gillibrand was an aberration. Grim prospects for Republican victories elsewhere made the 20th — with a 67,456 active voter advantage in party registration — appear to be as good a GOP redoubt as any. Throw in a wealthy, self-financing Republican candidate and a district that encompasses at least four media markets and you practically guarantee a broken spending record.

In a state that has become infamous for gerrymandered congressional districts, the 20th — stretching from Saranac Lake in the north to Millbrook and Hyde Park in the south, to the Southern Tier town of Sidney in the west — might best be viewed as three panhandles in search of a pan.

A slight detour here for those who have forgotten high school civics class: congressional district boundaries shift every decade following the decennial census and reapportionment by congress of the 435 house seats among the 50 states. The process of drawing boundaries to encompass equal numbers of constituents is left to the legislatures of individual states, a smooth enough drill if your legislature is, well, functional.

In Albany, however, the last three redistricting cycles have coincided with legislatures divided by party and geography. In the case of the last redistricting in 2000-2002, deeply divided. Consequently, a map of New York which naturally breaks down into neat, logical regions has been jig-sawed into a puzzle of pseudo-fractals and jagged rorschach blots.

All of this is about to change. With both houses of New York’s legislature and the executive branch held by the same political party for the first time since the 1970s, the redistricting machinery is about to run a lot faster, and might just result in a long-overdue return to cohesive districts in the wake of next year’s census.

Redistricting is a quintessentially political process and there are basically three rules for a single political party remapping congressional districts:

Rule #1: Keep your party’s incumbents safe. If reapportionment robs your state of one member of its delegation (as will happen to New York in 2010), make sure the seat is pulled out from under someone from the other side of the aisle.

Rule #2: Divide and conquer. If a geographically unified base of support for the opposing political party can be distributed among separate districts with larger safe populations of your own party, get out your meat cleavers.

Rule #3: If that hostile voting block is too large to be safely subsumed by friendly districts, then isolate and ignore it.

How these rules will affect the future of New York’s 20th Congressional District will largely depend on the outcome of the balloting on March 31st. One thing is certain in any case. With the special election this year, and an immediate reelection campaign in 2010 followed by a brand new race for a potentially radically redrawn district in 2012, this contested terrain will continue to be very expensive property for the incumbent.

Come back tomorrow for the Almanack’s modest proposal for a redrawn congressional district that neatly encompasses the entire Adirondack Park.