An enumeration district is a geographic area determined for purposes of taking the census. In one city there may be many enumeration districts, so once you enter a city, county, or state, you can narrow your results by entering street level information, or investigate enumeration district maps, or descriptions.
P wave. 1. a longitudinal earthquake wave that travels through the interior of the earth and is usually the first conspicuous wave to be recorded by a seismograph. Also called primary wave. Compare L wave, S wave. The P wave is admitted to be the wave of auricular contraction. p wave.
S waves and P waves are the two types of seismic waves produced by all earthquakes. P waves are primary waves because they arrive at seismic reporting stations first. These shear waves are secondary waves because they travel at slightly slower speeds and are the second set of seismic waves recorded on seismographs. Scientists use the difference in time to determine the earthquake focus and epicenter.