Location Referencing and Mapping Resources
- U.S. Agency for International Development (USAID) Office of U.S. Foreign Disaster Assistance (OFDA) field team members are often required to record and communicate location information, tasks that must be performed efficiently, unambiguously, and with sufficient precision. In addition, field team members may be provided detailed location information at times and required to navigate to the place of interest. This appendix provides a basic reference to assist in that effort and provides guidance on references and resources available to assist field teams with geographic information including, but not limited to, maps, satellite imagery, and locations of humanitarian points of interest.
- Note: Place names are often general knowledge among humanitarian responders; however, political sensitivities regarding place names and administrative boundaries may exist. Ask the Response Management Team (RMT) or OFDA Geographic Information Unit (GIU) for guidance on the names officially recognized by theU.S. Government (USG).
A. How To Reference Location
Before collecting location information, consider the needs of your primary and secondary audiences. The main issue to be resolved is the required level of precision. Does the information you are collecting need to be reported/displayed at a state or province level (low level of precision), at a town or neighborhood level (medium level of precision), or is a specific address or set of coordinates required (high level of precision)? Although your initial audience may require only a low level of precision, often the same information is later required at a higher level of precision.
Although precise information can be made more general, general information cannot be made more precise; therefore, USAID/OFDA recommends that you collect the information with the highest level of precision reasonably possible without adding a significant risk or burden to the team. Precise information can be aggregated for use in broader analyses or strategic level planning while still serving field-level utility, thereby satisfying multiple needs.
Low level of precision location information is gathered at a broad scale, such as the state or province level. Information gathered at this level is suitable for analyses at a broad scale, such as at the OFDA/W level.
Medium level of precision location information is gathered at a town or neighborhood level. Although more informative than low precision location information, medium precision location infor-mation is often too general to be useful at the field level.
High level of precision location information can comprise addresses in urban environments, landmark navigation from known points, or coordinates.
- Address. Many countries employ systems to supply unique addresses to buildings and homes. Talk to colleagues that have this local knowledge to determine if this option is avail-able. Augmenting address information with one of the other techniques may be advisable, depending on your audience.
- Landmark Navigation. In many cases, describing the location of a point of interest in terms of its distance and direction from a known point is sufficient, e.g., "A spontaneous inter-nally displaced persons (IDP) settlement was established 8 km from Kalima on the road to Shabunda." Key information conveyed is that this distance is an "over the road distance," as opposed to "as the crow flies." Providing all the informa-tion that makes this information unambiguous, such as the specific road segment and distance and units of measure, is also important.
- Coordinates. The most precise way to communicate location is with a complete latitude and longitude record, often referred to as a "lat/long." Another coordinate system that may be encountered in the field is the Military Grid Reference System (MGRS). Both systems divide the earth into grids; however, significant differences exist between the two (see "Coordinate Referencing System" below).
Obtaining detailed imagery for your area of interest to facilitate gathering location information with a high level of precision may be possible. An added benefit of using imagery is that it may be an important means of monitoring the area should access be cut off in the future.
In rare cases, high precision information might be considered sensitive or, as in the case of IDP camps during conflict, might place vulnerable populations at risk of further violence. As part of the USG, field teams must protect this information if acquired and use appropriate discretion when collecting.
2. Coordinate Referencing Systems
Latitude/longitude coordinates can be displayed in three formats without changing the location or precision of the point being referenced. These formats are degrees, minutes, seconds (DMS); decimal minutes (DM); and decimal degrees (DD). The following examples represent the same location.
- DMS: N 27°15’12" E 120°45’58"
- DM: N 27°15.2’ E 120°45.967’
- DD: N 27.25333° E 120.7661°
The following formula can be used to convert DMS to DD.
DD = degrees + (minutes+seconds/60)/60
Most global positioning system (GPS) units, however, can make these conversions.
Latitude/longitude is a Cartesian coordinate system with the Equator being 0° latitude and the prime meridian being 0° longitude. Coordinates south of the Equator and west of the prime meridian can also be represented by negative numbers (-). Thus, S 27.25333° W 120.7661° could also be referred to as - 27.25333° - 120.7661°.
The Military Grid Referencing System (MGRS) is explained in detail in the margin of maps produced by the military. Each component of an MGRS coordinate contains information on a progressively smaller grid read from left to right. For the coordinate 16SFL456987, the 16S represents an area stretching from the Equator to the South Pole, FL represents a small portion of that area, and 456987 represents a smaller area of the FL grid. In the field, an MGRS coordinate may often be reduced for more efficient communications (e.g., 456987 versus. 16SFL456987). This typically occurs when the entire area of interest lies within the larger grid designated by 16SFL. Note that 456987 indicates a 1,000 m by 1,000 m grid area and may not be sufficiently precise for navigation. By adding two digits, the precision can be improved to a more useful 100 m by 100 m area; adding two more digits further increases the precision to 10 m by 10 m. Therefore, each additional pair of digits within the MGRS coordinate increases the precision of the area represented by a factor of 100.
Precision of the
16S FL 123 123
16S FL 1234 1234
16S FL 12345 12345
Converting between systems ensures the ability to use maps and data provided from all sources. Field teams may receive location information in many formats, and the ability to identify these locations on maps can be invaluable. In most cases, the simplest way to convert between formats and referencing systems is to use the GPS units included in the field communications equipment cache. The GPS will change all stored points to the reference system selected by the user. Coordinate conversion can also be accomplished by using maps that have dual grid systems. Most maps produced for the military contain both referencing systems described here.
Differences between the latitude/longitude and MGRS coordinate systems are displayed in table E-1.
Table E-1. Comparison of Latitude/Longitude and MGRS Coordinate Systems
Divides globe into degrees, minutes, and seconds
Divides globe into grid system based on meters
Coordinate describes an exact point
Coordinate describes a grid cell or area
Can be made more or less specific by including or removing significant digits
Can be made more or less specific by including or removing significant digits
Standard coordinate system for civilian users
Standard coordinate system for military users
Provided by all GPS units
Provided by all GPS units
Example: N 27°15’12"
B. Mapping Resources
1. Getting Started
The RMT and/or GIU can provide access to the full range of mapping resources for field missions. In many cases, the best available maps may be in the field. Team members are encour-aged to actively seek maps within the region and explore local sources such as municipal authorities, United Nations agencies, NGOs, and local universities.
If an RMT is activated, it will manage requests for maps before and during deployment. The RMT must coordinate such requests because it will have the most complete inventory of what is available, ensure follow-through, and combine all requests to provide a full understanding of field mapping needs. If an RMT is not activated, the GIU will manage these requests directly.
The GIU provides geographic information support for OFDA/W, field teams, and partners. A member of the GIU is always included on RMTs, and mapping experts can be contacted at all times to respond to field needs. The GIU maintains a significant stock of map resources and interagency agreements to ensure access to all available resources. GIU staff or other mapping specialists can deploy as part of field teams as technical spe-cialists when requested by the field team.
In some cases, maps provided to field teams will have distribution limitations placed on them. These maps, although not classified, should not be provided or shown to non-USG personnel. Maps in this category should be marked clearly with LIMDIS (Limited Distribution) or FOUO (For Official Use Only). In certain situations, these limitations can be relaxed by petitioning the producers of the map and presenting a clear and compelling justification. In all cases, maps produced for, provided to, or purchased by the field team are property of the USG and must be treated as such. All maps should be left with an appropriate partner or returned to OFDA/W for storage and reuse.
2. Map Products
Reference maps, such as tourist maps and topographic maps, are used for navigation or general geographic awareness. Reference maps of many types are available to field teams and can either be acquired directly from local sources or through OFDA/W. Often maps acquired in the field exceed the quality of those available at OFDA/W. Should this occur, consider providing a copy to OFDA/W so that all parties use the same maps.
Thematic maps attempt to illuminate a specific issue or issues related to the humanitarian crisis, affected population, or geographic area, such as situation maps, program activity maps, and natural hazard maps, respectively. These products are often created from information provided by the field teams and are intended to broaden the understanding of the readers to the geographic realities of the situation. OFDA and other organizations produce custom maps displaying aspects of the humanitarian situation that are often posted online or available in field coordination centers. Custom maps can be produced for field teams on request.
Satellite imagery may be available from commercial satellites that can now collect imagery of sufficient detail to produce quick road maps of urban areas, provide initial damage assessments, or monitor displaced persons camps. Imaging satellites can detect features smaller than 1 square meter that can, in certain circumstances, provide a unique and useful perspective on areas of humanitarian interest. As with maps, field teams are encouraged to request imagery when appropriate and potentially useful. Manipulation of the imagery requires specialized training and software. A request for imagery support will typically result in a report, table, or map containing information about the features of interest. Atmospheric (clouds, dust, and haze) and technical constraints can delay or deny the collection of satellite imagery. If possible, urgent needs for overhead analysis, especially in the case of damage assessment, should be managed in-country with aircraft.