In competing against large companies, it usually pays to know as much as possible about their marketing strategies. You may be able to get some clues from the publications where they spend their advertising dollars. One inexpensive source of such information is Space Analysis Systems Inc., based in Huntingdon Valley, Pa. The company offers a service called SpaceTrak that monitors ads in more than 300 trade and specialty magazines. For $2, SpaceTrak will search its database and identify the market categories your competitors are targeting. For an additional $2 each, SpaceTrak will also provide individual reports showing where a specific competitor ran its ads and how much space it bought in the past two years.