Our site focuses on plants, animals, and fungi that grow in the Chicago Region, but identification keys can be written for any group of objects. For example, here's a simple key to four vehicles on a Chicago street last week. Start at step "1." and pick one of the two vehicle descriptions:
 1. Does the vehicle get over 40 miles per gallon? If so, go to step 2.
 2. Vehicle has four wheels and an engine – Toyota Prius
 2. Vehicle has two wheels and no engine – Mountain bicycle
 1. Does the vehicle get less than 40 miles per gallon? If so, go to step 3.
 3. Vehicle large, blocky, seats at least 6 people – Hummer
 3. Vehicle small, streamlined, seats 2 people – Corvette Stingray
Keys can sometimes offer more than two choices at each step. Here's one with three at the first step, which identifies some of the famous large buildings in Chicago:
 1. Is the building red? – CNA Plaza
 1. Or, is the building black? If so, go to step 2.
 2. Is the building a skyscraper? If so, go to step 3.
 3. Is this the tallest building in Chicago (and the USA)? – Sears Tower
 3. Is this the third tallest building in Chicago? – John Hancock Center
 2. Is the building much wider than tall? – McCormick Place
 1. Or, is the building white? If so, go to step 4
 4. Home of 20 million biological and anthropological specimens? – The Field Museum
 4. Home to a company that sells $4 billion of chewing gum per year? – Wrigley Building
This key to buildings can be rewritten so that the set of choices for each step are adjacent to each other. The key looks a bit different but functions the same way:
 1. Is the building red? – CNA Plaza
 1. Or, is the building black? If so, go to step 2.
 1. Or, is the building white? If so, go to step 4
 2. Is the building a skyscraper? If so, go to step 3.
 2. Is the building much wider than tall? – McCormick Place
 3. Is this the tallest building in Chicago (and the USA)? – Sears Tower
 3. Is this the third tallest building in Chicago? – John Hancock Center
 4. Home of 20 million biological and anthropological specimens? – The Field Museum
 4. Home to a company that sells $4 billion of chewing gum per year? – Wrigley Building
