Optimal Travel Speed

This is your scan radius - Light green will find Pokemon for your Sightings list, and dark green will put them on your map to capture.

This is your scan circle - Since your scan radius is 200m, you actually scan a circle that's 400m across.

The scanner refreshes every 10 seconds. - If you walk at a rate of 2.5 miles per hour (4kph) for a minute, you'll generate a series of scans that look like this. There is a lot of overlap, and you're not going to miss anything in this area.

Wolfram Alpha says that people jog at about 7.5mph (12kph) - Jogging at this rate will scan a wider area with almost no Pokemon slipping through.

If you're riding at 20mph (32kph) you'll travel 90 meters between scans. - Your Sightings list won't miss much, but about 1/3 of the pokemon in your direct path will not appear on your map on your first pass. This is a slow speed for a car, but a fast speed for a bicycle.

30mph (48kph) - Now you're moving 130 meters between scans. You're missing out on half of the pokemon in your path, and the "Sightings" list is starting to develop small gaps.

40mph (64kph) - Your "Sightings" list is still showing you everything that's directly in your path, but it misses quite a bit just to your left and right.

60mph (97kph) - Now, you're moving 27 meters per second. You are leaving large gaps between scans. Anything that shows up in your Sightings list should just be ignored. It won't show up on your map unless the driver turns around.