Dortmund (51.5136° N, 7.4653° E) and Gelsenkirchen (51.5177° N, 7.0857° E) are right in the centre of the Ruhr valley -- separated by a mere 30km (18 miles) -- but the sporting geography has shifted so much in Germany's most football-crazed region that Borussia and Schalke 04 barely find themselves in the same league.
Whereas the Black and Yellows can reclaim top spot from Bayern Munich -- for 24 hours at least -- and boost their Bundesliga title credentials with a home win in the 154th Revierderby on Saturday, Schalke find themselves fighting for survival in Germany's top flight.
Dortmund have won eight league titles to their rivals' seven, but all Schalke's successes came before the birth of the Bundesliga in 1962 and they are no longer the region's No. 1 club. Ever since Dortmund claimed their first championship in 1956, a triumph for either against the hated neighbours has come with its own, delicious reward, irrespective of repercussions in the table.
On this occasion, however, the huge -- if asymmetrical -- importance of the result for both parties will make this fiercely tribal dispute even more fractious than usual and millions in Germany will tune in at 3:30 p.m. CET to witness the hostilities play out live on free-to-air TV.
"You know that Saturday will be war," Schalke midfielder Benjamin Stambouli said. "Winning the derby is the best feeling in the world. It's our chance to give back to our supporters in these difficult times."
BVB captain Marco Reus put the task in more prosaic terms. "We simply have to thump Schalke to stay in contention," the Germany international declared.
Dortmund are entitled to feel optimistic. Their 4-0 away win at Freiburg last week was not quite as convincing as the scoreline suggested but came with a rare clean sheet and a sprinkling of goals of extraordinary quality. The demoralising effect of BVB's 5-0 defeat in Munich three weeks ago has proved very short-lived and belief has returned.
Schalke, by contrast, are in the middle of a rotten run that has brought only two league wins since the winter break. The slump led to the departures of sporting director Christian Heidel and coach Domenico Tedesco, but there has been no real improvement since last year's runners-up brought back club icon Huub Stevens, 65, as interim manager at the beginning of the month.
Indeed, the famously gruff Dutchman's ultra-defensive style has arguably made a team low on guile and creativity blunter and even more unwatchable; Schalke have mustered a mere 32 goals in 30 games, 40 fewer than Dortmund. If it was not for the rank incompetence of the teams below them, the troubles of the team in 15th place would be much greater.
As it is, a six-point gap with four games remaining to Stuttgart, who look set to contest the relegation playoff against the third-best team from the second division, offers a modest degree of comfort. But Schalke's stock has fallen so low that even their enemies have taken pity on them.
"I don't want them to go down, the Bundesliga needs Schalke and the derbies," BVB CEO Hans-Joachim Watzke told Sport-Bild, though his empathy was rather limited. "I find the suggestion that they could save their season with one game a little ridiculous. Their aim is to stay up. If it's up to me, they'll do so -- but not against us."
Dortmund have worked hard to be in a position to patronise the Revier's former top dogs. Schalke didn't just dominate German football in the 1930s and early 40s, they played an early, stylish version of possession and passing football that rendered most opponents utterly helpless. But that is a lifetime ago.
It's now 61 years since Schalke won the Meisterschaft (championship), since when the club have developed a deeply fatalistic streak and an unhealthy obsession with hard work on the pitch that runs contrary to their illustrious past. Following Heidel's failed attempt to bring back former glories, they face their umpteenth reboot next season.
Dortmund, on the other hand, are so firmly established as the league's second-biggest side after staving off insolvency in 2005 that their fortunes are not materially affected by the outcome of this title race. Whether they will manage to win their first championship since 2012 has little bearing on their status as Champions League regulars and purveyors of pleasing attacking football with gifted youngsters.
In truth, Dortmund have outgrown the local rivalry. But as last season's breathtaking 4-4 draw at the Signal Iduna Park showed, when Schalke claimed a point despite conceding four unanswered goals in the opening 25 minutes, logic does not necessarily prevail in the emotional thunderstorm that this fixture generates.