For most of this year, a battle has been brewing over the proposed "Mission Moratorium" and how to address a shortage of affordable places to live in the neighborhood that's been called ground zero for San Francisco's housing crisis.

Supervisor David Campos, who represents the Mission District, first publicly floated the idea of halting market-rate residential construction in May. His legislation fell two votes short of a nine-vote supermajority it needed to pass the Board of Supervisors in June. But by that time, a coalition of community groups was already crafting what would become Proposition I.

The measure's language is deceptively simple: If Prop. I passes, the city would not issue permits for 18 months in the Mission for either new market-rate housing developments (what Prop. I supporters call "luxury housing") or renovations of buildings containing five or more units. It would also halt demolition, renovation or conversion of certain industrial businesses zoned as production, distribution and repair. The measure would allow the Board of Supervisors, by a majority vote, to extend the development halt for an additional year.

It also requires the city to create a comprehensive housing plan by early 2017 that would ensure at least half of all new housing in the Mission be affordable for low-, moderate- and middle-income earners.

The proposition's implications, however, are somewhat complex and involve the soft science of economics and the fluid housing market.

Supporters and opponents agree that the Mission District has been ravaged by San Francisco's housing crisis. Long-term residents of the neighborhood have been priced out in droves, to the point that Latino residents no longer make up a majority of the population. A report released Tuesday by the city's budget and legislative analyst projects that, if current trends continue, Latinos will make up less than a third of Mission District residents in 2025.

"It’s going to become a boring neighborhood," said Roberto Hernandez, a resident and Mission District organizer affiliated with many groups, including Our Mission, No Eviction. "You’re not going to have the mariachi. You’re not going to have the person selling churros, the lady selling flowers on the corner, and just that vibrant Latin-American feel that the Mission has -- it’s going to be gone. It’s going to disappear."

The report found that the district is losing its economic diversity as well. From 2000 to 2013, low-income Mission District households earning less than $35,000 per year increased by about 900. The neighborhood shed 600 moderate-income households and added more than 1,000 households earning $150,000 or more.

Prop. I opponents point to another report, this one released in September by the city controller's office. They say despite the Mission's troubles, halting development there will only make things worse. The controller's report found "a temporary, 18-month moratorium would lead to slightly higher housing prices across the city, have no appreciable effect on no-fault eviction pressures and have a limited impact on the city's ability to produce affordable housing during the moratorium period."

That's because city law requires market-rate developers to either sprinkle some affordable units in any given project (12 percent of the total units), build more affordable units in another location (20 percent), or pay a fee for developing below-market-rate units.

"If we stop market-rate development, it will absolutely dry up those funds, funds that are being currently slated to be used in the Mission District to build affordable housing," said Supervisor Mark Farrell. "It is simply the wrong approach."

But Campos, who supports the ballot initiative after his legislative attempt failed, said the city's affordable housing fee hasn't worked to actually develop the units the Mission needs to keep home prices and rents in the neighborhood down to something resembling sanity.

"I don’t think it’s working because the concept of letting developers not build on site is a flawed one," Campos said. "I’m all for building more, but we’re not going to take that argument to its logical next step in a way that’s realistic. ... We’d have to double the size of San Francisco. We’d have to build another city on top of this city."

That point comes from the budget and legislative analyst's report, which applied national and statewide housing needs estimates to San Francisco. It found that for city housing costs to have stayed on par with prices nationwide, San Francisco would need to have added 459,000 housing units between 1980 and 2010. There are less than 400,000 units in the whole city.

But, as opponents point out, there's no disagreement over the debacle that is San Francisco's housing market and the need to do something. The question is what.

"We all know that there is an issue around affordability, not only in the Mission District but across the city," Farrell said. "From my perspective, we need to be building more housing at all income levels. ... We need to make sure that we build more housing in our city, more housing in the Mission District, and that’s the only way we’re going to be able to alleviate the housing crisis that we have right now."

Roberto Hernandez has heard that argument. He said he's been hearing it for years while his friends and neighbors have been forced out of the Mission.

"It's been coined by the developers and the mayor: 'Build, build, build, build.' But that's for the rich and not for the everyday folk. ... It's not for the people in the Mission. It's not for people in San Francisco."