In order to gain a better understanding of the scale of the universe, it is helpful to begin by calculating the size and scale of something that is easily measurable. As a useful introductory exercise, map the classroom in two dimensions at different scales so that the skills of linear measurement, unit conversion and metric conversion are mastered before distances between objects become difficult to imagine. Divide the class into small groups. Give each group graph paper, rulers, pencils and construction paper. Ask each group to create a map of the room. Assign one or two people in each group to measure the dimensions of the room, the teacher's desk, the doorways and other objects in the classroom. Ask the students to pick a scale (as in one block on the graph paper equals one foot) and to draw the classroom on the paper. They should then create construction paper furniture and doors, also to their scale. It is sometimes useful to have two groups use the same scale so that they can compare the size of their "furniture." Ask the students whether the furniture in their map would "fit" in the maps of other students who have used the same scale. This question stresses the importance of consistency within scale. Then ask the students to create a smaller scale of their own maps. This project can be done in two ways: 1) by going back to the original measurements, or 2) by scaling down the current map scale. At this point, you can also ask the students to convert their scales from imperial (feet and inches) to metric (meters and centimeters) or vice versa. (The conversion factor is 2.54 centimeters to one inch.) This exercise will show the students that scaling is arbitrary, meaning that any scale can be chosen, but demonstrates that a convenient scale, such as 1 foot is equal for each graph paper block, will expedite their work. It also shows that scales can be changed at will, as long as they are changed consistently. If this activity is completed, the maps should be saved; as described in a later activity, they can be used to depict the expanding universe.