The sixth sextant.

It calls to mind a Decembrists album title, or the artifact Indiana Jones seeks on the far side of a pit of snakes.

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On a more prosaic note, it’s Portland’s newest address designation.

The City Council voted Wednesday to add a sixth member, South, to the city’s existing quintet of address areas: North, Northeast, Northwest, Southeast and Southwest.

The new South Portland occupies a strip of land shaped like a pointer finger along the west bank of the Willamette river.

The area includes roughly 10,000 addresses and properties in the South Waterfront, Collins View and Riverdale neighborhoods, including parts of the Oregon Health and Sciences University campus and Lewis and Clark College.

The river is the eastern boundary of the South District, while Southwest Naito Parkway and the Tryon Creek State Natural area are the western boundary.

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Residents in the South Waterfront neighborhood and the Portland fire marshal have pushed for the change, citing a wonky — yet serious — problem.

Many addresses in the area begin with a leading zero, confusing first responders, delivery people and mapping apps.

“For whatever reason, a lot of people don’t see a zero when it’s the first, leading number in an address,” said commissioner Dan Saltzman at a hearing last week on the proposed change. “When seconds matter, it’s important for our first responders, our 911 call dispatchers and call takers to know exactly which address they’re responding to,” he said.

The reason for the confusing zero: Portland’s famous address grid that is based on streets running in straight lines.

Address numbers are supposed to decline toward zero as they approach the city’s East-West dividing line, the Willamette River.

But in the South Waterfront neighborhood, the river swings just a bit to the East, meaning the address numbers hit zero before they reached the river — which is why the leading zero was tacked on there. (Hat tip to this blogger for the explanation).

The new addressing system will eliminate the leading zero for addresses that have them. For example, 0715 SW Bancroft Street will become 715 South Bancroft Street.

Other streets and properties will only see a minimal change, the removal of a W from the directional portion of their address.

Starting in May 2020, the city will begin a five-year transition to the new addressing system, posting street signs with the South designation. Street signs marked Southwest will be removed in 2025.

The U.S. postal service will continue to deliver envelopes and packages addressed using either the old or new directional system.