Higher buildings, smaller lots, twice the number of apartments and townhomes — all stacked neatly inside the boundaries of the county's 10 cities.

That's how Ventura County should accommodate the inevitable population growth of 200,000 more people by 2030, according to the results of a countywide mapping workshop held in June.

The results were presented Wednesday at a workshop in Ventura inviting further community discussion of how the county should build housing, businesses, roads and mass transit networks over the next few decades. A similar session will be held today in Simi Valley.

"The real question is how do we accommodate this population growth without going outside city boundaries, which no one seems to want," said Ron Bottorff, a member of the Ventura County Civic Alliance, which hosted the workshops.

"To do that right, we have to consider higher densities than we're used to building. That's the trade-off versus spreading."

About 135 people participated in the June mapping session. Participants were asked to build growth scenarios for the county.

Their final vision, called "Hold the Line," called for:

n Expanding multifamily housing to 58 percent and shrinking single-family housing to 33 percent. Currently, single-family homes dominate Ventura County's housing landscape at 75 percent.

n Rezoning vacant commercial land within city boundaries to residential use.

n Building up, not out. Currently, there is vocal opposition in several communities to new developments higher than two or three stories.

n Aggressively developing vacant areas — or infill — within cities, reducing the need to build new roads and infrastructure.

Attendees at Wednesday's session included policymakers, politicians and others concerned with the county's future growth patterns.

Ventura City Manager Rick Cole said current attitudes will present a challenge.

"The answer we have in Ventura is that we'd like to see infill development, but in someone else's neighborhood," Cole said.

Patrick McIlhenney, a Ventura architect, said he would like to see more multiple-use development such as building a two-story building with apartments atop a business. But resistance to that concept is strong in many cities, he said.

"For any developer, considering multiple use in Ventura County right now is a gamble," McIlhenney said.

Those who attend the workshops are being asked to fill out a survey for more input. The Civic Alliance, an initiative of the Ventura County Community Foundation, hopes to use people's comments as part of a document that would be finished by the end of the year.

The whole process is modeled after similar community discussions and "consensus documents" that have been used to map out the long-term growth of the region.