Objective: When using global positioning systems (GPS) to assess an individual's exposure to their environment, a first step in data cleaning is to establish minimum GPS 'inclusion criteria' (a set of rules used to determine which GPS data are able to be included in analyses). Care is needed at this stage to avoid any data exclusion (data loss) systematically biasing results in terms of characteristics of the environment and participants. The extent of potential systematic bias in sample retention due to GPS data loss and application of GPS inclusion criteria is unknown. The aim of this study was to describe differences in sample size and socio-demographic characteristics of the retained sample when applying three different GPS inclusion criteria. The study assessed 7-day GPS data collected from children (aged 9-13 years) recruited from nine schools in Auckland, New Zealand as part of the Kids in the City study. Results: Participants from ethnic minorities and those attending schools in lower socioeconomic areas were disproportionately excluded from the retained samples. This highlights potential equity implications in basing the assessment of exposure - which ultimately influences research results on the relationship between environment and health - on non-representative GPS data.