Finding the most active brokers, developers and investors in last year’s booming real estate environment was even more of a challenge than in previous years, because so many people were so active.

Commercial leasing activity, in particular, was very brisk, with nearly all the submarkets in L.A. County ending up with lower vacancy rates at the end of the year than at the beginning and in some places, such as the Westside, with vacancies nearly nonexistent and rents going through the roof.

Architects had plenty of work with a spate of major hospital, school and public-works projects. Developers took a cautious but still active approach to new buildings, while private investors found themselves with lots of available deals after real estate investment trusts largely disappeared from the market.

That said, here’s how the Business Journal determined this year’s award winners:

– Information for the most active developer category was provided by representatives of the development firms themselves.

– Cushman & Wakefield Inc. provided a list of the most active investors in L.A. County.

– Builders of the largest office, industrial and retail projects to break ground last year were determined through research by Cushman & Wakefield, as well as representatives of the firms themselves.

– Data for the residential broker categories were supplied by the brokerage firms. Brokers were asked to include only home sales in L.A. County that closed in 1999.

– The Meyers Group provided information to determine the largest new residential projects and fastest-selling ones.

– Architectural and interior design firms were ranked by their 1999 billings for projects done in L.A. County. This information was provided by the firms themselves.

– For commercial brokers, winners were determined by information submitted by the brokerage firms. In each category, the firm was asked to nominate its top candidate according to the following rules:

The broker could only take credit for 1999 deals involving properties in L.A. County. The individual broker could take credit for only that portion of the deal that was commensurate with his or her share of the total commission paid on that deal. The broker could only include deals that fit in the category for which he or she was nominated.