"You'd be lost without us," said John Bartholomew V. It's a slogan used by the Bartholomew family, which has been making maps since 1826, but he spoke, clearly, for 500 mapmakers from 44 countries who will be meeting at the University of Maryland through next Wednesday.

Sitting in the building's large auditorium, listening to talks simultaneously translated into French and Spanish like a United Nations session, the Ninth International Cartographic Conference heard that their profession, which is probably as old as the art of writing, still has a lot of unfinished business:

Forty percent of the earth's surface is not yet adequately mapped - let alone the far side of the moon and the depths of the ocean.

Unmapped areas are found not only in the jungles and deserts, but in the heart of some of the world's largest cities. "Large areas of my home state, Wisconsin, are not covered by modern maps," said Arthur Robinson, former president of the International Cartographic Association and dean of American cartographers.

Inadequately mapped areas are now being covered at a rate of only 1 percent per year - at a cost of about $1 for each member of the world's population, according to Batholomen.

Meanwhile, because of modern technology, new information for inclusion in maps is arriving at a much faster rate than it can be handled.

Cartographers argue that the need to change old maps to include new data is as important as the need to cover indequately mapped territory.

Maps are being made by no fewer than 40 agencies of the United States government - with only minimal conflict and duplication, according to William Radinski of the U.S. Geological Survey.

Cartographers seem to be people who know exactly where they are, but they also seem to wonder whether the rest of the world knows. "I tried to look up 'cartographers' under 'C' in the Columbia Encyclopedia," said F. J. Ormeling, president of the ICA, "and we weren't there. I finally found us under 'maps' - between 'maple syrup' and 'Mao Tse-tung.'"

Looking en masse like a faculty meeting on an old-fashioned Ivy League campus, cartographers are members of a profession that has nearly completed its transition from an art to a science. Heirs of men who paid in blood for the opportunity to inscribe "Here bee tygers" on their charts, and who liked to fill in unexplored territories with pictures of dragons and giants, they have now reached the point where much of their basic information is radioed in from a satellite and fed into a computer, which instructs a "plotting" machine on what lines to put where.

"The field has been totally revolutionised," said Robinson. "In some cartography labs, there are no pens anymore. A lot of maps are being produced without anyone putting ink on paper anywhere in the process. The information is coming in by the bucketful. We used to have to scrounge for it. But now, the tough decision is what to leave out."

The need for maps is growing, the mapmakers feel, with the increase in the amount of mappable information ("anything that has spatial distribution," according to Robinson).Not only mountains and highways but air lanes and ocean bottoms, population patterns and water resources, types of plant growth and minerals and religious affiliations need to be understood, and a map format is often the best way to keep track of them. Once new dimension in demand is the three-dimensional map for the blind, stamped in sturdy plastic with Braille inscription. (The Boston subway has one, for example).

The ICA's next meeting will be held two years from now in Tokyo; the last one was Moscow, 1976, and delegates have fond memories of Russian hospitality ("vodka at 10 a.m.!") and a solid respect for Russian work. "They have a great big area to map, and they've done it better than we have," said one American. "At least in terms of coverage," added a foreign friend, and the American agreed that American maps have more details. It is a crime for ordinary Russian citizens to own some types of topographical maps that can be bought anywhere in the United States.

Cartography is now a recoganized academic field in American universities, according to Andrew McNally III, whose family name is almost synonymous with "map" in the United States, "but the best cartographers we have had for the last 50 years have come from the old countries."

McNally also believes that mapmaking still can be "partly an artistic process" in "the use of symbols, the way you put words on a map."

With old family rival Bartholomew warmly agreeing, McNally said that he believes governments are entirely too active and commercial in mapmaking today - unfair competition for private mapmakers who can't afford the expensive (and inartistic) automated equipment used for some government maps.

He may have a point. According to one government spokesman, U.S. civilian agencies are now spending $500 million per year producing 400 different kinds of maps and charts. That put us at more than double the percapita world average, without counting military and private activities. So why is it still so hard to find Adelphi Road?