title: Quantifying Distance Overestimation From Global Positioning System in Urban Spaces.
abstract: OBJECTIVE
  To investigate accuracy of distance measures computed from Global Positioning System (GPS) points in New York City.
  
  
  METHODS
  We performed structured walks along urban streets carrying Globalsat DG-100 GPS Data Logger devices in highest and lowest quartiles of building height and tree canopy cover. We used ArcGIS version 10.1 to select walks and compute the straight-line distance (Geographic Information System-measured) and sum of distances between consecutive GPS waypoints (GPS-measured) for each walk.
  
  
  RESULTS
  GPS distance overestimates were associated with building height (median overestimate = 97% for high vs 14% for low building height) and to a lesser extent tree canopy (43% for high vs 28% for low tree canopy).
  
  
  CONCLUSIONS
  Algorithms using distances between successive GPS points to infer speed or travel mode may misclassify trips differentially by context. Researchers studying urban spaces may prefer alternative mode identification techniques.
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Mooney
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sheehan
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Garazi
authors.initials: G
authors.lastname: Zulaika
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Rundle
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Kevin
authors.initials: K
authors.lastname: McGill
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Melika R
authors.initials: MR
authors.lastname: Behrooz
authors.affiliation: Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.
authors.forename: Gina Schellenbaum
authors.initials: GS
authors.lastname: Lovasi
mesh_terms: D061827:Dimensional Measurement Accuracy; D004777:Environment; D040362:Geographic Information Systems / Q000295:instrumentation*; D006801:Humans; D009519:New York City; D014195:Travel; D014505:Urban Population; D016138:Walking