Appendix C: Determining Latitude and Longitude

There are many ways that monitoring groups identify and describe the location of sampling sites. Commonly, monitoring sites are described by stream name and geographic location, such as Volunteer Creek at Oak Road or Volunteer Creek behind the picnic area in Volunteer Park. Often these description are accompanied by an assigned station number (i.e. VC001, VC002). Some programs use river miles—the distance from the sampling station to the stream's mouth—as an additional identifier.

Maps, in many forms, are also typically used to help identify sites. These include road maps, state/county maps, aerial maps, hand-drawn site maps, and topographic maps. Section 3.1 in Chapter 3, Watershed Survey Methods, discusses the various types of maps used by monitoring programs and provides information on obtaining topographic maps from the U.S. Geological Survey (USGS). The most accurate way to identify sampling locations is by determining their latitude and longitude. Any volunteer program that wishes to have its data used by state, local, or federal agencies, or that plans to enter its data into a Geographic Information Systems (GIS) either now or in the future, must provide latitudes and longitudes for its sampling locations. EPA's STORET water quality database, for example, requires latitude/longitude information before any data can be entered. Section 4.1 in Chapter 4, Macroinvertebrates and Habitat, briefly describes using a global positioning system (GPS) to determine latitude and longitude. This hand-held tool is used in the field and receives signals from orbiting satellites to calculate the lat/long coordinates of the user. New tools are continuously developing to help you locate your sites. For example, EPA's Surf Your Watershed web page ties in with the U.S. Geological Survey's Names Information System to provide latitude and longitude information for locations throughout the U.S. These locations include bridges, schools, rivers, parks, and more. Visit this feature of Surf Your Watershed at www.epa.gov/surf/surf_search.html for more information. Latitude and longitude can also be calculated manually. To do this, you will need a topographic map, a metric ruler, and a calculator. A worksheet for calculating latitude and longitude based on the EPA Region 10 Streamwalk protocol is presented below.

Latitude and Longitude Latitude and longitude are defined and measured in degrees (°), minutes ('), and seconds (''). There are 60 seconds in a minute and 60 minutes in a degree of latitude and longitude. Latitude (lat) is the angular distance of a particular location north or south from the equator. Latitude lines are called parallels. Longitude (long) is the angular distance of a particular location east or west of some prime meridian (usually Greenwich, England). Longitude lines are called meridians.

Worksheet for Calculating Latitude and Longitude (PDF, 21.7 KB)

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