LandScan 2000 Documentation
Introduction
The LandScan data set is a worldwide population database compiled on a 30" X 30" latitude/longitude grid. Best available census counts (mainly at sub-national level) were apportioned to each grid cell based on probability coefficients, which are based on proximity to roads, slope, land cover and nighttime lights. LandScan 2000 has been developed as part of the Oak Ridge National Laboratory (ORNL) Global Population Project for estimating ambient populations at risk.
Methodology
To create LandScan, census counts (usually at sub-national level) were distributed to 30" by 30" grid cells using interpolation based on composite probability coefficients. The composite probability coefficients are relative likelihood of population existence in cells due to road proximity, slope, land cover, and nighttime lights (Dobson et al. 2000).
Roads -- weighted by distance from major roads.
Slope -- weighted by the favorability of slope categories.
Land Cover -- weighted by type, with exclusions for certain types.
Nighttime Lights -- weighted by frequency.
The resulting coefficients are weighted values, independent of census data, which can then be used to apportion shares of actual population counts within any particular area of interest. Coefficients vary considerably from country to country even within a particular region. Control totals can be based on any administrative unit (nation, province, district, minor civil division) or arbitrary polygon for which census data are available. The resulting population distribution is normalized and compared with appropriate control totals to ensure that aggregate distributions are consistent with census control totals.
Source Data
The foundation of the LandScan population database is worldwide census data obtained from the 1994 Global Demography Project (Tobler et al., 1995). Conducted by the National Center for Geographic Information and Analysis (NCGIA), the project developed a 5' X 5' resolution population database (from 57o N to 72o N). Aggregate census data and demographic characteristics (age/sex) by country and sub-national area were obtained from the United Nations Statistical Division, and updated through 2000 through the International Programs Center of the United Stated Bureau of the Census.
The probability coefficient for each cell in this database was calculated based on publicly available databases offering worldwide coverage of roads, slope, land cover, and nighttime lights at scales of 1:1,000,000 or larger and resolutions of 1 km. or finer. The sources of these databases are as follows:
Roads
To provide universal coverage of road networks, LandScan has incorporated the National Imagery and Mapping Agency's (NIMA) Vector Smart Map (VMAP) series (formerly Digital Chart of the World). VMAP-Level 1 (at 1:250,000 scale) was employed for every tile available. VMAP-0 (at scale 1:1,000,000) was used in areas not covered by VMAP-1. NIMA’s VMAP data is publicly available and covers the entire world at 1:1,000,000 scale and 1:250,000 for much of the world.
Slope
LandScan employs NIMA's Digital Terrain Elevation Data (DTED) Level 1, 3 Arc Second Terrain Data for slope data. DTED-0 with 30 Arc Second resolution is employed wherever finer resolution data is not available. The proportion of land suitable for settlement was calculated within each grid cell.
Land Cover
For global land cover data, LandScan utilizes the U.S. Geological Survey's (USGS) Global Land Cover Characteristics (GLCC) database. This data set is derived from Advanced Very High Resolution Radiometry (AVHRR) satellite imagery at 1 km. Resolution (Loveland, 1991). http://edcdaac.usgs.gov/glcc/glcc.html. The land cover database was further refined using VMAP-1, NIMA’s Controlled Image Base (CIB) and/or NIMA’s scanned maps.
Nighttime Lights
LandScan employs new radiance-calibrated Nighttime Lights of the World light frequency data processed and provided by NOAA's National Geophysical Data Center (NGDC). The use of this dataset enabled the detection of small towns and villages and discrimination of density density levels within large cities. Further information on Nighttime lights can be found on the U.S. Defense Meteorological Satellite Program (DMSP) at http://www.ngdc.noaa.gov/dmsp/dmsp.html.
Detailed source documentation on LandScan is available at http://www.ornl.gov/gist/projects/LandScan/SIMPLE/smaps.htm
Data Accuracy
The precision and accuracy of the LandScan data set are hard to determine due to the wide variety of sources and methods used to compile the data. Verification of spatially explicit global population databases like LandScan is inherently limited by the difficulty of establishing a suitable reference database for purposes of comparison. However, a number of steps were taken towards verifying the data, including:
Verification based on the best available census counts.
· Extrapolation of results from areas with good reference data to areas with poor reference data.
· Use of remote sensing (non-LandScan data) to pinpoint the indicators of population in areas of question.
Verification, validation, and sensitivity analyses of input data.
These verification and validation studies have been conducted routinely for all regions of the world, and have been conducted more extensively for portions of the Middle East and the southwestern United States.
References
Dobson, J. E., E. A. Bright, P. R. Coleman, R. C. Durfee, and B. A. Worley, 2000. A Global Poulation Database for Estimating Population at Risk. Photogrammetric Engineering & Remote Sensing 66(7).
Loveland, T., J. Merchant, D. Ohlen, and J. Brown, 1991. Development of a land-cover characteristics database for the conterminous U. S. Photogrammetric Engineering & Remote Sensing 57(11), pp. 1453-1463.
Tobler, W. R., U. Deichmann, J. Gottsegen, and K. Maloy, 1995. The Global Demography Project. Technical Report No. 95-6. National Center for Geographic Information and Analysis. UCSB. Santa Barbara, CA, 75p.
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