An airport's noise environment is defined and illustrated by the Day-Night Average A-Weighted Sound Level metric known as DNL. The DNL was introduced by the U.S. Environmental Protection Agency (EPA) as a method for predicting the effects on a population of the long-term exposure to environmental noise. The DNL metric is required under 14 CFR Part 150 as the single system for measuring aircraft noise impact and for determining land-use compatibility.

NEMs (sometimes called "noise contours" or "noise contour maps") do not illustrate flight paths. They simply illustrate where most of the aircraft noise is. The number of aircraft heard and the noise level on any given day will depend on which runways are used, weather, flight schedules and community background noise. Aircraft altitudes will depend upon the type of aircraft and the destination or origin of the flight.

NEMs typically depict the DNL 65dB contour, as this is generally identified by federal guidelines as the threshold of significance for aviation noise and other sources of community noise. In general, most land uses are considered to be compatible with DNLs of less than 65 dB.

Nashville's NEMs were generated through use of the Federal Aviation Administration's computerized Integrated Noise Model (INM), which determines the aircraft sound levels associated with an average annual day's activity.