Presentation at the 2006 Active Living Research Annual Conference
Active living studies have shown that enjoyable scenery and shops and other destinations within close proximity to one’s home increases physical activity (walking) in a residential neighborhood. This study examines the relationship between greenness, destinations and walking behavior using both objective (GIS and Normalized Difference Vegetation Index (NDVI)) and subjective (survey) measures.
Our objectives are to understand the:
1) Relationship between objective and subjective measures of greenness and walking behavior.
2) Relationship between objective and subjective measures of proximity to destinations and walking behavior.
3) Mediating effects of quality of life and neighborhood satisfaction on walking behavior.
GIS Network Analysis. We used GIS Network Analysis to identify residential parcels within the city limits of Seattle, that are within walking distance to different destinations using the existing street network. Walking distance was defined as 0.4 miles, which has been shown to be the outer limit that people will walk on a regular basis. We chose sixteen destinations (restaurants, libraries, parks, etc.) to include in the GIS analysis. For each destination in the city, a service area was created representing the 0.4-mile distance surrounding that specific destination. The service areas for these different destinations overlapped in some areas and not in others, creating an entire city map of areas of residential parcels with high walkability (many destinations to walk to within 0.4 miles) and areas of residential parcels with low walkability (few destinations within 0.4 miles).
NDVI Analysis. To measure greenness throughout the city, we used the NDVI, which is calculated from remotely-sensed satellite data. NDVI has shown to be correlated with ecosystem parameters such as vegetation cover and bird diversity. In order to account for the inherent variability in NDVI values over the scale of a walkable area, we used an average NDVI for the area within walkable distance.
Survey. To triangulate the objective measures of walkability of neighborhoods in Seattle, a mail questionnaire was sent out to 3,300 Seattle residents. We selected addresses for the quality of life survey from GIS network data of residential parcels within the Seattle city limits using stratified random sampling, selecting parcels of high (>80th percentile) and low (<20th percentile) NDVI in each of low (zero to two destinations within walking distance), medium (three to five destinations within walking distance) and high (six to 12 destinations within walking distance). We were careful to maintain approximately representative proportions of single- and multi-family housing in each of these six strata.
The survey collected data about perceptions of what destinations the resident felt were within walking distance, walking behaviors, the greenness of their neighborhood, neighborhood satisfaction, quality of life and health (BMI was calculated), as well as demographic information.
The GIS Network results showed that within the City of Seattle, 27% of parcels were within walking distance of zero to two services, 45% within walking distance of three to five services and 28% within walking distance of six to 12 services. There was a subtle but significant negative relationship between the walkability score and the NDVI (R2=0.22, P<0.0001). At the time of writing the abstract, the survey was being administered. Preliminary results regarding walking behavior, quality of life and health will be completed in time for the conference in February 2006.
This study has shown that, in general, there is a trade-off between walkability and greenness of the environment. This is not a particularly surprising result, as one would expect that more destinations within walking distance means more buildings and roads resulting in fewer trees. However, we were able to identify neighborhoods in all levels of walkability that have high or low greenness which show that there are neighborhood planning and design practices available that will retain a large portion of greenness in neighborhoods and destinations within easy walking distance from one’s home. Our survey results will show whether these areas of greenness and high walkability interact to impact people’s quality of life, neighborhood satisfaction and health. In addition, this study has used a unique combination of objective and subjective measures to help further active living research.