accuracy of iphone locations.pdf

Transactions in GIS, 2009, 13(s1): 5–26 Research Article Accuracy of iPhone Locations: A Comparison of Assisted GPS, WiFi and Cellular Positioning Paul A Zandbergen Department of Geography University of New Mexico Abstract The 3G iPhone was the first consumer device to provide a seamless integration of three positioning technologies: Assisted GPS (A-GPS), WiFi positioning and cellular network positioning. This study presents an evaluation of the accuracy of locations obtained using these three positioning modes on the 3G iPhone. A-GPS locations were validated using surveyed benchmarks and compared to a traditional low-cost GPS receiver running simultaneously. WiFi and cellular positions for indoor loca- tions were validated using high resolution orthophotography. Results indicate that A-GPS locations obtained using the 3G iPhone are much less accurate than those from regular autonomous GPS units (average median error of 8 m for ten 20-minute field tests) but appear sufficient for most Location Based Services (LBS). WiFi locations using the 3G iPhone are much less accurate (median error of 74 m for 58 observations) and fail to meet the published accuracy specifications. Positional errors in WiFi also reveal erratic spatial patterns resulting from the design of the calibration effort underlying the WiFi positioning system. Cellular positioning using the 3G iPhone is the least accurate positioning method (median error of 600 m for 64 observations), consistent with previous studies. Pros and cons of the three position- ing technologies are presented in terms of coverage, accuracy and reliability, fol- lowed by a discussion of the implications for LBS using the 3G iPhone and similar mobile devices. 1 Introduction Reliable location in