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Methods for determining the uncertainty of population estimates derived from satellite imagery and limited survey data: a case study of Bo city, Sierra Leone.

Hillson R, Alejandre JD, Jacobsen KH, Ansumana R, Bockarie AS, Bangura U, Lamin JM, Malanoski AP, Stenger DA - PLoS ONE (2014)

Bottom Line: For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images.Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size.We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs.

View Article: PubMed Central - PubMed

Affiliation: Information Technology Division, Naval Research Laboratory, Washington, District of Columbia, United States of America.

ABSTRACT
This study demonstrates the use of bootstrap methods to estimate the total population of urban and periurban areas using satellite imagery and limited survey data. We conducted complete household surveys in 20 neighborhoods in the city of Bo, Sierra Leone, which collectively were home to 25,954 persons living in 1,979 residential structures. For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images. We used bootstrap statistical methods to estimate the total population of the pooled sections, including the associated uncertainty intervals, as a function of sample size. Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size. We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs.

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Rooftop area-based population estimations for Njai Town using invalid and valid scale factors.(A) Non-convergent rooftop area-based population estimate with 0.50 (blue) and 0.95 CIs (red). Samples were drawn from the Njai Town dataset of 127 residences only, but the scale factor  was set to the rooftop area for all 269 structures (). (B) Convergent rooftop-based population estimate with 0.50 (red) and 0.95 (blue) CIs. Samples were drawn from the Njai Town dataset of 269 residential and non-residential structures, and  was set correctly set to . Source: residential survey data and digitized rooftop areas,  = 37,358 .
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pone-0112241-g007: Rooftop area-based population estimations for Njai Town using invalid and valid scale factors.(A) Non-convergent rooftop area-based population estimate with 0.50 (blue) and 0.95 CIs (red). Samples were drawn from the Njai Town dataset of 127 residences only, but the scale factor was set to the rooftop area for all 269 structures (). (B) Convergent rooftop-based population estimate with 0.50 (red) and 0.95 (blue) CIs. Samples were drawn from the Njai Town dataset of 269 residential and non-residential structures, and was set correctly set to . Source: residential survey data and digitized rooftop areas,  = 37,358 .

Mentions: SIM04 and SIM05. Figure 6 shows the imagery and map of the Njai Town and Reservation sections. Residential structures are denoted in red; non-residential structures are denoted in blue. Figure 7 compares the rooftop-area population estimator under two different scenarios, both using DS03. In SIM04 only the 127 residential records are sampled – that is, all records drawn have 1 or more individuals as residents – but the total rooftop area is equal to the rooftop area of the combined residential and non-residential structures ( = 37,358 m2). This results in a total population estimate for Njai Town that is much greater than the true value. In SIM05, the population estimate draws on both residential and non-residential structures, so in some records the number of individuals is 0. This time the estimator converges correctly.


Methods for determining the uncertainty of population estimates derived from satellite imagery and limited survey data: a case study of Bo city, Sierra Leone.

Hillson R, Alejandre JD, Jacobsen KH, Ansumana R, Bockarie AS, Bangura U, Lamin JM, Malanoski AP, Stenger DA - PLoS ONE (2014)

Rooftop area-based population estimations for Njai Town using invalid and valid scale factors.(A) Non-convergent rooftop area-based population estimate with 0.50 (blue) and 0.95 CIs (red). Samples were drawn from the Njai Town dataset of 127 residences only, but the scale factor  was set to the rooftop area for all 269 structures (). (B) Convergent rooftop-based population estimate with 0.50 (red) and 0.95 (blue) CIs. Samples were drawn from the Njai Town dataset of 269 residential and non-residential structures, and  was set correctly set to . Source: residential survey data and digitized rooftop areas,  = 37,358 .
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4232376&req=5

pone-0112241-g007: Rooftop area-based population estimations for Njai Town using invalid and valid scale factors.(A) Non-convergent rooftop area-based population estimate with 0.50 (blue) and 0.95 CIs (red). Samples were drawn from the Njai Town dataset of 127 residences only, but the scale factor was set to the rooftop area for all 269 structures (). (B) Convergent rooftop-based population estimate with 0.50 (red) and 0.95 (blue) CIs. Samples were drawn from the Njai Town dataset of 269 residential and non-residential structures, and was set correctly set to . Source: residential survey data and digitized rooftop areas,  = 37,358 .
Mentions: SIM04 and SIM05. Figure 6 shows the imagery and map of the Njai Town and Reservation sections. Residential structures are denoted in red; non-residential structures are denoted in blue. Figure 7 compares the rooftop-area population estimator under two different scenarios, both using DS03. In SIM04 only the 127 residential records are sampled – that is, all records drawn have 1 or more individuals as residents – but the total rooftop area is equal to the rooftop area of the combined residential and non-residential structures ( = 37,358 m2). This results in a total population estimate for Njai Town that is much greater than the true value. In SIM05, the population estimate draws on both residential and non-residential structures, so in some records the number of individuals is 0. This time the estimator converges correctly.

Bottom Line: For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images.Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size.We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs.

View Article: PubMed Central - PubMed

Affiliation: Information Technology Division, Naval Research Laboratory, Washington, District of Columbia, United States of America.

ABSTRACT
This study demonstrates the use of bootstrap methods to estimate the total population of urban and periurban areas using satellite imagery and limited survey data. We conducted complete household surveys in 20 neighborhoods in the city of Bo, Sierra Leone, which collectively were home to 25,954 persons living in 1,979 residential structures. For five of those twenty sections, we quantized the rooftop areas of structures extracted from satellite images. We used bootstrap statistical methods to estimate the total population of the pooled sections, including the associated uncertainty intervals, as a function of sample size. Evaluations based either on rooftop area per person or on the mean number of occupants per residence both converged on the true population size. We demonstrate with this simulation that demographic surveys of a relatively small proportion of residences can provide a foundation for accurately estimating the total population in conjunction with aerial photographs.

Show MeSH