Like so many other significant developments in the New York real estate business, this one was triggered by a proposed rent increase.

During the inflationary years of the 1970's landlords were trying to pass on rising costs to tenants, each in proportion to the amount of space they occupied, recalled Robert F. R. Ballard, an executive vice president of Cushman & Wakefield, the brokerage and services company.

The problem was that few agreed on what percentage of the total rent increase should be assigned to each tenant, because there was no accepted compilation of building sizes and layouts.

So Mr. Ballard and some assistants set about collecting information on every major building in Manhattan that was not completely owner occupied, and they published the Directory of Manhattan Office Buildings in 1978. The book, which was priced at a whopping $79.50, contained pictures, layout plans and floor sizes for each of the 500 buildings listed, along with their ages and heights and the names of the owner, architect and principal tenants.

The book was the predecessor of the computerized databases that now provide up-to-date information for landlords, tenants, brokers and investors. Several ambitious efforts in the field did not survive the implosion of the dot-com companies, but others have become well established.

The larger national players, as well as some specialized companies that focus on investors, are increasingly adding analytic capabilities to their services, so users can probe the databases in search of economic opportunity. The addition of analytical tools is a conscious emulation of what the Bloomberg terminals did in disseminating financial information for the markets for bonds and other debt securities. Other smaller players have sought out niche markets, such as supplying listings for economic development agencies or for print publications' Web sites that carry the brand of the host organization.

"A lot has happened over the last two years," said Andrew C. Florance, president of CoStar Group, one of the most prominent of the real estate information services. "Our long-term goal was not to be a listings service, but to try to quantify what is happening in commercial real estate markets." Traditionally, he said, real estate has been a localized business with information on market conditions and transactions often hard to find.

Based in suburban Washington, CoStar says it is attempting to supply data on more aspects of the real estate market by adding, among other things, information on building sales and prices to data on vacancy rates, direct and sublet spaces and asking rents. The company collects its data at 34 offices in the United States and Britain and has about 875 employees.

Mr. Florance said CoStar, which has acquired 14 data reporting companies over the last few years, is attempting to impose order on the chaotic industry by setting standards for how information is collected and reported. This is a new development for an industry where each brokerage company has had its own standards for what types of buildings to monitor and how to present data.

In New York, where the number of buildings changes only slowly over time, each of the large brokerage firms reports different figures for vacancy rates and average asking rentals. For example, the current office vacancy rate in Manhattan varies from 10.39 percent to 14.6 percent, according to various reports, while the average asking rent has been reported at anywhere from $32.37 a square foot annually to $43.39 a square foot. The disparities can be caused by things as simple as the failure of building managers to return telephone calls from researchers seeking information on leasing, industry executives say, or disagreements as to what buildings are grouped in Class A, Class B and Class C.

Other differences are caused by varying definitions. Some firms will track only buildings over a certain size; others include smaller properties. Submarket definitions vary as well. "Midtown South" is in the eye of the beholder, and brokerage companies tend to hold on to old definitions to keep their statistics comparable over time.

Having accurate information about the state of the market is important for those making investment decisions, particularly about starting new construction, Mr. Florance said. He said it is generally agreed that when the vacancy rate in an office market reaches 15 percent, starting new buildings is unwise.

The vacancy rate hit that level in 1990 in the Washington area, he said, but no one could be sure at the time "because the reported vacancy rate was 8 to 23 percent." The result, he added, "was massive overbuilding."

He said that because many large brokerage companies use CoStar data to establish base lines, while doing specialized research on their own, the variations among reports is less than in the past. "They are within a few points of each other these days," he said.

But some research executives say that it takes too long for CoStar to collect and publish data for the information to be completely useful to brokers trying to make deals and that the company's data does not go into enough detail. Other researchers say the economic interests of companies that market services to landlords and tenants alike tend to use data collection methods that have an influence on the final results.

No company can buy all the information it needs about real estate on open markets, said Maria Sicola, the senior managing director for research for Cushman & Wakefield, which downsized its research department in 2000 during the dot-com boom.

"We were swept up in the e-commerce notion that information was going to become a commodity available to anybody," she said. "In about two months we realized that was not going to be the case."

By then, however, the company had laid off about 30 of the approximately 100 people on its research staff and sold its current database at the time to RELocate, a successful leasing research company that focused on the New York market.

The database was used to create RealtyIQ.com, which tried to compete with CoStar, but collapsed when revenues did not come close to meeting the debt incurred in setting up a national system. It was one of several ambitious reporting projects that failed or never got started after investors soured on the profit potential of Web-based services.

Bruce Z. Weissberg, who ran RELocate for about 10 years before selling to the investors backing the RealtyIQ venture, said a service like CoStar's has become essential, particularly for smaller brokerage companies that cannot afford research staffs. But he said it is hard for users to know how accurate and timely the information is. "CoStar said it calls properties on a monthly basis, which is actually hard to do," he said. "In any case, the information is 30 days old. When we had a different database, brokers bought both."

Mr. Weissberg said he is currently associated with D. G. Hart, a Manhattan brokerage, and is managing a redevelopment project in Chicago.

Ms. Sicola said Cushman & Wakefield had retained its historical database after the sale and a research staff of about 70 people, and rebuilt its research capability based on information not available from public sources. "We have 800 brokers and 100 appraisers, and they are constantly meeting with owners, building agents and tenants," she said.

"They add information to the database about who has space that may not be on the market yet and tenants who may need space," she said. "For example, we know there is as much as 8 million square feet of shadow space out there — that is, space that is not on the market but could be. We know where that space is, but it is not reported by any service."

ACCOUNTING rules and practices have recently been changed with the intent of limiting the reporting of losses that cannot be accurately measured, but these changes are not likely to force this shadow space into the open, according to Gregory A. Tosko, an executive managing director in Insignia/ESG's consulting operation.

Existing rules force publicly owned companies to take losses against current earnings when they sign subleases at rents less than they are paying the landlord. But companies are not allowed to take charges for unused shadow space as a means of improving future earnings reports, Mr. Tosko said.

Still, investors would be wise to keep an eye on companies that keep piling sublet space on the market, Mr. Florance observed. "Often," he said, "a big sublet is a flag signaling that a company is in big trouble."

Joseph R. Harbert, the chief operating officer of Insignia/ESG's metropolitan New York region, said he buys basic information from CoStar, but also relies on his company's brokers to get closer to the current market. "We think of brokers as the best single source of information, so we do broker-centric information gathering," he said. While listing services can provide asking rents for properties, brokers who are shaping the deals are in the best position to know what the actual taking rent was that resulted from negotiations.

Mr. Harbert said that while CoStar's reporting system, which includes 550 researchers making telephone calls backed up by a people in a fleet of vehicles making on-site inquiries, has improved over the years, information from brokers doing deals will almost always be closer to the market. "We think we have an edge of two to four weeks in time, and greater accuracy," he said.

Building managers have a greater incentive to give full information to a broker than to a researcher, because the broker may bring a tenant to the property, Mr. Harbert said. Nevertheless, he noted that his company had a 15-member research staff to fill in information gaps left by the brokers.

Brokers active in a market are more sensitive to changes in building classifications, said Matthew Barlow, an executive managing director of Julien J. Studley, a brokerage that has traditionally represented tenants. Buildings in New York are generally grouped in three grades: Class A, for the newest and best equipped; Class B, for older properties in less choice locations; and Class C, for the least desirable space.

"Of 1,100 buildings listed by a third-party data service, we had different classifications on 300, which can significantly alter the statistics," he said, adding that Studley brokers had a meeting last month during which the classification of 35 buildings was changed. The criterion? "If 55 out of 60 brokers say a building is Class B, then it is a B building," he said.

Brokerage companies that represent landlords and property managers have an incentive to describe the market as more robust than it may actually be, said M. Myers Mermel, the chief executive of TenantWise.com, a Web-based service that combines listings with brokerage activities.

"They have a conflict because they represent landlords as well as tenants," he said, an argument echoed by other tenant brokers and firmly rejected by their competitors who represent interests on both sides of the space leasing process.

Mr. Ballard, who prepared the book that was the precursor of the databases now available for New York, said his original objective was to settle disputes over rent escalations. "The landlords wanted escalations and the tenants were supposed to pay their proportionate share of the increase," he said. "The landlords' accountants sent out bills with the increases each year, but the bigger tenants didn't buy that. At the time, in many cases neither the landlord or the agent knew how many total square feet were in a building, so it was hard to peg the correct percentage for each tenant."

With the blessings of his superiors at Cushman & Wakefield, Mr. Ballard approached the publisher McGraw-Hill with his proposal. It was accepted, and the publisher assigned an editor and an assistant to help gather data.

The project entailed long hours at the city's Department of Buildings, going over floor plans and recording when buildings opened and who designed them. The legwork also included visiting buildings, dealing with often-uncooperative landlords and literally measuring the floors.

This was still the age of paper, so each building had its own folder containing plans, photographs and clippings from industry publications. Some notable properties, like the Chrysler Building, required more than one folder, Mr. Ballard said.

In all, it took about 3,000 hours of work over two years to complete the project. Cushman & Wakefield's research department was a result of the book, he said. "It happened slowly, starting with one person," he said. "But the company wanted to be known as a real estate services company that really knew the market, so it grew over a 20-year period to what it is today."

Mr. Ballard recalled that he had had no interest in updating the book as information changed and new buildings were added. "I was worn out," he said.

One company that did was Yale Robbins Inc., whose magazine-style Office Buildings publications largely followed Mr. Ballard's format. "Bob Ballard did the first book, and he did a great job as a one-man show," said Henry Robbins, executive vice president of the company. "We wanted to do a joint venture with Bob, but I guess Cushman & Wakefield did not want him to do it."

THE Robbins company has since added Web-based information to its printed publications, with a listing service called MrOfficeSpace.com. Unlike most data services, which charge users for information, MrOfficeSpace.com offers its information free, while charging listers for displaying enhancements beyond basic data.

Robbins has also developed a business of hosting the office space listings for publications like Crain's New York Business and business groups like the Alliance for Downtown New York. Another smaller player, Cityfeet.com, has developed a niche hosting space listings for the Web sites of newspapers, including nytimes.com.

Two years after the dot-com related shakeout, the real estate information services appear to be financially stable, if not hugely profitable. CoStar, which is publicly traded, has reported that it is profitable as measured by earnings before interest, taxes, depreciation and amortization, an accounting standard preferred by real estate companies. It has not yet reported a profit according to the more demanding standards used by most major corporations.

Others report they are cash flow positive, meaning they have more money coming in than going out, although not profitable in a fully accounted sense. Many other listings services exist, including the San Francisco-based LoopNet.com, which claims to have the largest number of listings and users.

The Ballard and Robbins publications and their electronic descendants have largely been marketed to brokers and renters and users of office and retail space.

Meanwhile, other electronic information services have been developed that are aimed primarily at real estate investors. Once again, the model is the Bloomberg service, which combined data on securities trading with automated analytic capability so that prospective investments could be quickly ranked against one another.

One of the leading players in this sector is Reis Inc., a New York based company that sells Web-based reports on the financial condition of various markets around the country and of individual properties and the terms of sales transactions.

Lloyd Lynford, the president of Reis, said he started publishing paper reports on real estate markets in 1980 but has migrated to a Web-based system as the technology has evolved. "The last year and a half has been a time of evolution," he said. "Despite the crash and burn of the dot-coms, Web-based delivery of information on commercial real estate to lenders and investors has grown in response to evolving markets."

He said real estate investment managers need timely and accurate information because they compete for capital with managers who invest in stocks and bonds, where access to information is almost instantaneous. "We need a Bloomberg for real estate," Mr. Lynford said.

He said the company focuses on 50 major real estate markets in the United States and collects its basic data quarterly, but is emphasizing adding tools so that its 9,000 desktop users can quickly analyze their portfolios or prospective purchases in response to changes in market conditions. "Real estate is valued as an income stream, so you want to be able to figure the impact of a change in interest rates," he said.

The Reis database includes information on some individual properties as well as general market conditions and includes likely financial outlooks for them. For example the database includes estimates that the 2.5-million-square-foot former Port Authority warehouse at 111 Eighth Avenue, between 15th and 16th Streets, which is now mostly an office building, will have a net cash flow of $57.9 million this year. This is expected, the database says, to rise to $58.6 million by the end of next year and $59 million by 2005.

Mr. Lynford admits that the figures, which seem amazingly precise, are based on a standard set of assumptions, which can be changed and the results automatically recalculated. Indeed, a page is attached to the financial display giving a user a long list of variables to be changed if the user thinks his own estimates are closer to reality.

The largest category of customers for Reis services is lending institutions, because most real estate transactions are financed with far more debt than equity, Mr. Lynford said. Using the system, a loan officer can enter the loan terms and derive an estimate of a property's worth and estimate the likelihood of a default by the owner.

These estimates will become increasingly important as lenders have to conform to new international standards for holding financial reserves against potential losses. In general, the higher these reserves, the lower a lender's profitability.

"What is the probability of default? Is it 2 percent or is it 8 percent? Bankers need to know the answer," Mr. Lynford said.

Although automated information systems are improving, Robert M. White, president of Real Capital Analytics, which sells information services to investors, said his group collects its own data on $8 billion of sales in progress. "We maintain a proprietary database because there are no standards out there," Mr. White said. "What is a community shopping center? No one agrees.

"We do sales comparables, including who the players were in a deal, how much was paid and the other details," he said. "There was no other data available, so we had to create it."