Environmental approaches to promoting physical activity in youth and adults show much promise; however, current knowledge regarding measurement of environmental determinants of physical activity is quite limited. Although a number of studies have demonstrated that environmental attributes are associated with physical activity, there have been few systematic attempts to develop reliable and valid objective physical environmental measures.  In the proposed measurement study that will focus on topic #2 in the ALPES CFP, an interdisciplinary research team from the fields of physical activity/public health, geography, landscape architecture, and parks and recreation will develop and evaluate objective measures of outdoor recreational settings where walking, bicycling and other linear activities are performed.  Study sites will be six recreational areas located in urban, suburban, and rural settings in Massachusetts and will include linear parks, rail-trails, outdoor tracks, and other types of parks.  Selection of measurement domains will be based on ecological models and social cognitive theory, current evidence from public health/physical activity studies, practice guidelines from landscape architecture, and formative work conducted by the research team.  Existing geographic information systems (GIS) data layers, observation/auditing of facilities, and other methods will be used to develop objective measures of facility characteristics that will be integrated into a GIS. At each recreational area, measures pertaining to both site (e.g., intrinsic to the park, trail) and situation characteristics (e.g., contextual variables, such as land-use within a ½ mile buffer of a linear park) will be developed.  Interdisciplinary input will be sought at all phases of the project, including initial definition of measures, collection of observational data, assessments of reliability, development of GIS methods and database(s), and a final summary critique of study methods, measures, and costs.  The primary study aims are to: 1) develop objective GIS measures of the physical characteristics of six diverse recreational areas where recreational walking and other physical activities can be performed, including sub-component areas defined by GIS; 2) evaluate the reliability of objective measures of physical characteristics obtained via observation; 3) assess the relative advantages and disadvantages of the different methodologies we use to objectively characterize outdoor recreational spaces, including direct observation, use of GIS data layers, analysis and integration of orthophotographs into GIS databases; and 4) comprehensively document GIS and other study methods (e.g., observation of facilities) and disseminate key findings on measures and methods through a variety of channels.  This study will build on ongoing research at the Harvard Prevention Research Center directed at understanding the influence of both physical and social environments on physical activity and overweight.