What is the geocoding in Did You Feel It, and how is it used?
We have the capability of adding geocoded maps for certain larger events with many hundreds (or thousands) of responses. To do this, we take the addresses that people provide when they fill out our questionnaire, and send them to TeleAtlas, a company that turns regular street addresses into precise latitude and longitude coordinates (generally 6 digits of accuracy, enough to distinguish the nearest block on a street). We then group nearby coordinates into regularly sized boxes, which are generally a few kilometers across, and calculate their intensities the same way we do for normal zip code maps.
To test this geocoding on your own address, try this interactive script. There are several advantages to using geocoding for maps, including greater precision in locating intensities and cleaner-looking maps (since zip codes tend to be very irregularly shaped). For rapid response to earthquakes, though, zip codes are still preferable - almost everyone knows immediately which zip cod they are in, whereas few people know their latitude and longitude (and especially not to the needed precision).Note that because roughly 5-10% of respondents do not leave their address, there are correspondingly fewer responses on a geocode map vs. a zip code map.