They can't ignore each other, so it's good that city Mayor Martin O'Malley and Baltimore County Executive C.A. Dutch Ruppersberger seem to be getting along.
They've huddled over how to handle the flood of telephone calls and invitations that chief executives receive. They've talked about how to get money from Annapolis.
This week, they announced a joint set of legislative priorities that attempts to tackle shared problems of crime and neighborhood blight.
The connection between two of the region's top elected officials is critical to the future of the city, the county and the state as a whole, political observers say.
"The relationship is vital," said Attorney General J. Joseph Curran Jr., O'Malley's father-in-law, who has watched both men in action for years. "The city has some problems, but they are solvable if you have cooperation. Cooperation is the key, and cooperation is contagious, and it makes you feel good that we are working together."
The relationship also offers the promise of political benefits. Ruppersberger would need strong city support to win the race for governor that he is widely expected to join.
O'Malley needs county assistance to counterbalance anti-city sentiment in Western Maryland and the Washington suburbs that weaken his chances for much-needed state funds.
On the surface, the two leaders have much in common. O'Malley, 37, and Ruppersberger, 54, are former prosecutors and former Democratic councilmen in their jurisdictions. Neither is afraid to say what's on his mind, and both have the energy to make 14-hour workdays look easy.
So it was natural that when O'Malley was elected in a landslide last fall, the two men looked to each other for assistance.
"Dutch came forward immediately and said if Martin would like help, I would really like him to be successful," said state Sen. Barbara A. Hoffman, a Democrat and chairwoman of the Senate Budget and Taxation Committee whose district includes parts of the city and county. "And Martin, to his credit, said that would be wonderful. When can it start?"
The relations could be more promising than those between Ruppersberger and O'Malley's predecessor, Kurt L. Schmoke, who joined the executive on issues such as a shared police radio system and school-reform legislation.
"Kurt and I really worked on major issues together," Ruppersberger said. "But Kurt's philosophy was a little different. He was not in there to change things the way Martin is.
"I think Martin has an agenda. He wants to change things. He is looking to reform the criminal justice system, which just isn't working right now."
Geography dictates that the mayor of Baltimore and the executive of Baltimore County share a similar agenda.
Baltimore County nearly surrounds the city, a configuration like no other in Maryland. The shared 30-mile border was drawn by mapmakers in 1918 after the city's final outward annexation.
Countless families have hopscotched over that line in the past three decades, in search of better public schools, safer streets and bigger backyards. These days, robbers, drug buyers and other criminals pass back and forth. The most recent vivid example was last week's fatal shooting of an off-duty county police sergeant at a Pikesville jewelry story. Four city men have been charged.
At the top of O'Malley's agenda is the region's crime problem. "The blood already has leaked beyond our borders," he said. "We realize that these are issues that impact the region as a whole."
The need for cooperation goes beyond keeping streets safe.
In the struggle for state funds, it's easy for the city to get swamped by Prince George's and Montgomery counties, which clamor for transportation and environmental dollars. There and in Western Maryland, many view Baltimore as a financial drain.
A strong alliance with Baltimore County and other neighboring suburbs gives O'Malley much-needed influence in Annapolis.
For Ruppersberger, who is prevented by law from seeking a third term as county executive, city support could help in a run for higher office.
"The county executive has said he is willing to help the city, possibly because he has his eye on the governor's office," said Matthew A. Crenson, a political science professor at the Johns Hopkins University. "It also shows that Baltimore County and Baltimore City are having the same kinds of problems."
O'Malley said Baltimore and other counties, such as Harford and Anne Arundel, are rallying behind his administration because he has presented an optimistic vision of the city.
"This administration actually believes there is something we can do with law enforcement and the criminal justice system," O'Malley said. "I think that everybody's so delighted that there's an administration that doesn't have a defeatist attitude about law enforcement."