1. Pick a part of a city that you are very familiar with and where the streets run at right angles.

2. Go to Google Maps. (http://maps.google.com) Enter the name of the city you chose in step one.

In the above illustration, Santa Monica, CA has been entered. Press Search Maps.

A map will appear.

3. In the lower left hand corner of the map is the map scale:

In the upper left hand corner is a slider for setting the scale. As you move the slider (the box with the minus sign, on the railroad track), the scale of the map will change.

With your mouse, move the slider up (towards the plus sign) until the scale at the bottom says 200 feet/50 meters, like this: .

Now move the image around until both ends of the 200 foot scale fall on identifiable points. Make a note of where those points are.

4. Print a copy of the map. The print command is at the upper right, above the map:

We will now mark out on the printed copy a 200-foot by 200-foot square with one of its corners on the corner of a city block. Unfortunately, Google doesn't include the scale on maps printed from it, so you now need your note about the ends of the scale. On the printed map, find the two points you identified as being 200 feet apart. Mark the distance between them on the edge of a piece of paper.

5. Choose a familiar corner of a city block. Using the marked paper, find the point 200 feet from the corner, going in one direction. Mark this point on the map you printed out.

6. Turn the paper 90° and measure 200 feet from the corner in other direction. Mark this point on the map you printed.

7. Draw a square with those 200-foot sides. It will be 92% of an acre (40,000 square feet, instead of 43,560). So extend the shaded area by about an extra tenth.

8. If a “hybrid” button is available at the upper right hand corner of the Google screen, click on it. The aerial view will give you an idea of where the lines you have drawn fall among real buildings.

If you possess a large-scale map of your city with a good scale, you can carry out a better version of the above project.

1. Referring to the map's scale, measure the width in feet of a familiar, rectangular, city block.

2. Divide 43,560 by your measurement. Call the result X feet.

3. Referring to the map's scale, measure off X feet along the length of the same city block.

4. Complete and shade the rectangle. It is 1 acre.

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Last revised: 21 March 2010.