Mapping the development of green in gardens over time: is your neighbour’s garden really greener?

Abstract. Private gardens are an important aspect of small urban green space and help provide a wide range of ecosystem services. This contribution is increasingly recognised and several local governments now stimulate residents to replace garden pavements with vegetation. Tracing such greening efforts is difficult, however, because of their small scale and absence in official mapping efforts. Therefore, we propose an approach to map the greening of gardens by analysing a time series of highly detailed aerial photographs. Our approach overcomes several challenges: the temporal variation in the green signal because of seasonal differences in green cover or shade, the small size of gardens and the obstruction of vision by overhanging trees. We present the results of this analysis and assess their accuracy by using a confusion matrix.