Recent work by architect Christopher Alexander suggests a new holistic approach to the measurement of landscape structure, based on properties of the relationships between coherent wholes. Measurement of these properties relies upon qualitative judgment and aesthetic perception, but can be quantified using ordinal scaling and tests of intersubjective agreement. I demonstrate how these holistic structural properties can be assessed through the use of both aerial and ground-level photographs, and describe initial results relating them to measures of biodiversity and ecosystem health for sites near Seattle, Washington. I am conducting quasi-double-blind surveys in which subjects use Alexander's properties to compare images of sites for which independently-obtained measurements of biodiversity and/or ecosystem health are available. In the first survey the images were aerial photographs of 1 km^2 landscapes, centered on locations with measured avian biodiversity, representing a range of land-cover types and development patterns. In the second survey the images are of urban and suburban stream reaches for which B-IBI data has been collected, and in the third survey the images are of fish-habitat restoration sites. Results from the first survey indicate that photographs judged higher in Alexander's properties correspond to locations with higher biodiversity at a frequency significantly greater than would be expected by chance (p <=0.05) for most subjects, and that intersubjective agreement is significantly better than would be expected by chance for most image pairs (p <=0.05). Preliminary results from the second and third surveys will be available by August 2007.