As entrepreneurs from all over pour into San Francisco to participate in the latest tech boom, rents are rising across the city. And one of the best ways to gauge that rise is to check out HotPads, the map-based housing search engine and listings service.

As it turns out, HotPads, the company, is part of this trend itself. The 20-person startup, which started as a tiny venture in Washington, D.C. in 2005, has just moved its headquarters to the Mission District.

“I’ve been trying to get back here for six years,” says co-founder Douglas Pope, whose first job after college (Notre Dame) was in this area.

HotPads uses its own mapping technology – back when the company started, Google Maps had not yet fully emerged from the laboratory, plus the search giant was not focused on mapping rental housing listings.

HotPads also offers additional layers of data, including neighborhood information, price comparison tools, school district and public transportation overlays, and so on.

In other words, the service tries to provide the kind of information you most need when you’re seeking a new place to live.

In recent years, HotPads has added in real estate listings, as well as vacation rentals, a neighborhood hotel finder and even foreclosure listings. A “heat maps” feature allows you to check out factors such as population density, household income, median age, and the median rent in a neighborhood you’re interested in.

Another feature is the “points of interest” that alerts you to nearby attractions.

Probably the most innovative feature allows users to “lasso” any area of a local map and draw their own customized search zones, which in a city like San Francisco, is enormously helpful because our neighborhoods vary almost block by block in the types of housing available.

Today, HotPads hosts some 400,000 rental listings nationwide, and 3.5 million “for sale” listings as well. The company partners with some 400 data-providers, and makes money primarily from banner ads plus paid “featured listings,” which show up on the map in bright red.

The site attracts around 3 million unique users and 4.6 million visits per month. One of the side benefits of reaching this scale is the company’s ability to issue reports on trends in the housing market, including one supplied to 7x7 that reveals that the cost of renting a studio apartment in the city has risen by 12 percent over the past year, and the cost of renting a one-bedroom has gone up by ten percent.

So, why did HotPads relocate here from the nation’s capital?

“We wanted the ability to work in a more consumer-web environment,” says Pope. “In Washington, there are plenty of entrepreneurs and engineers, but they are primarily focused on government contracts, defense work, and so on. Out here, there are many more companies like ours, and a much bigger pool of engineering talent focused on the consumer web.”

Like most, the company is hiring developers, and is holding an open house at its Valencia Street office this Thursday, August 25, to celebrate its arrival on the scene.

BTW, once they’ve settled in, maybe these guys can get to work on mapping another neighborhood factor, one of the most important ones to those of us who’ve lived in the city a long time, and that, of course, is the unique problem of our many micro-climates.