Relations between the city of Spokane and Spokane County have been so strained for so long that no election would seem complete without hearing candidates vow to mend them.

An overture that Spokane Mayor Mary Verner has extended, therefore, represents a breakthrough that should not be squandered. In a letter to all three Spokane County commissioners, Verner has suggested that their respective governments start to work this summer on an annexation strategy that would address the revenue concerns at the center of past tensions.

Land-use planning issues are complex and have critical impacts on government finances and many aspects of community life. If you never grasped the consequences of sprawl, it should be clearer now that driving to the mall burns up $4-a-gallon gasoline.

Hence, the 1990 Growth Management Act, which was adopted over strong opposition in mostly rural Eastern Washington, has provided an essential framework for deciding where development will go and which governments will be responsible for services.

But that hasn’t made it easy for cities to annex the property that has experienced urban development beyond city limits. Those fringe areas look identical to the cities they abut, but they lie in unincorporated areas and bolster county government’s tax base rather than the city’s. The law calls them urban growth areas and foresees their annexation.

Growth has intensified the pressure, but that’s not the only problem. The law limits the county’s property tax collections to 1 percent growth a year; the cost of delivering services grows much faster. The incorporations of Liberty Lake and Spokane Valley have helped shrink the rural area’s share of Spokane County’s population to 18 percent, lower than any of its peer counties.

Meanwhile, 70 percent of the county budget goes to criminal justice expenses, including courts and jails where volume is driven mostly by crimes committed within the city. No wonder annexation discussions bog down over where the county will get the revenue to meet its service-delivery obligations.

Last year, when Spokane finally completed the annexation of 135 acres of commercial property along North Division, it cost county government about $1 million a year in sales tax revenue. The county calls it cherry-picking, and when a judge approved it, a disappointed County Commissioner Mark Richard found a ray of consolation in her further ruling that the county may challenge such annexations in court. That was important, Richard said, “if we can’t get some kind of a long-term agreement.”

Verner, who wasn’t yet mayor during the contentious North Division annexation episode, has now opened the door to some kind of long-term agreement, one that finally respects the county’s budget concerns. Substantive planning negotiations are never easy, but the 433,000 people who live in Spokane County deserve an earnest effort by their elected leaders to make the effort.