Measure Urban land area in the Great Lakes Basin.

Purpose This metric assesses the presence of urban areas and metrics associated with urbanization in the Great Lakes Basin.

Features This metric offers information on the presence, location, and predominance of human-built land cover and can be used to provide information about how such land cover types potentially effect the ecological characteristics and functions of ecosystems in the vicinity. This metric can be tracked over time if necessary.

Limitations To conduct such measures at a broad scale, the relationships between land cover and ecosystem functions need to be verified. This measure will need to be validated fully with thorough field-sampling data, and sufficient a priori knowledge of such endpoints and the mechanisms of impact (if applicable). The development of indicators (e.g., a regression model) is an important goal, and requires uniform measurement of field parameters across a vast geographic region to determine accurate information to calibrate such models.

Interpretation "Urban Density" may be used to infer "land use", and may be used to infer general patterns of human activities. However, more direct measurements of human activities are possible (e.g., road density and human population). Urban Density affects can be more thoroughly explored and explained if they are linked to the functions of ecosystems (e.g., as it relates to surface water quality). Interpretation of this indicator is correlated with many other metrics and their patterns across the Great Lakes. Urban density affects on ecosystem functions should be linked to the ecological endpoint of interest, and this interpretation may vary as a result of the specificity of land cover types and the contemporaneous nature of the data. Thus, more detailed land cover specificity is required, which is currently under development by EPA/ORD.

Comments A thorough field-sampling protocol, properly validated geographic information, and other remote-sensing-based data could lead to successful development of urban density as an indicator of ecosystem function and ecological vulnerability in the Great Lakes Basin. This indicator could be applied to select sites, but would be most effective if used at a regional or basin-wide scale.

Metric Maps Remote sensing and GIS data have been used to directly map the extent of urban land, and other measures of urban activities, such as percent impervious surfaces, road density, and the presence of human habitation, as measured by the U.S. Census Bureau.