They are often dichotomous keys which means they only have two choices at each step. Sometimes they have more than two choices at each step and are not dichotomous. This enables taxonomists to research plant identification and how plants are related to each other.
Some examples are flower color, leaf shape, leaf margin and seed type.
In some areas you may need written permission to collect from the authorities. This is called a collecting permit. Some plants have small distribution ranges and others are widespread. GPS unit - a Global Positioning Unit uses signals from satellites orbiting the earth to give an accurate reading of the latitude and longitude at any point on the earth. This sort of plant is often small.