The region spans a swath from 5°N to 5°S latitude and 120°W to 170°W longitude. Source: Niño Region Map | Climate.gov
The shaded rectangle shows the region of the Pacific Ocean where the observed sea surface temperature is compared to average sea surface temperature. Data collected by two main methods:
Sometimes, research vessels that pass through the area will also take observations. The National Oceanographic and Atmospheric Administration (NOAA) uses this information monitor the current phase of ENSO.