Highlighting the trend within a cloud of points

Trends in scatter plot clouds could be difficult to appreciate. This is an intelligent way of showing the (mean) trend hidden within the messy cloud of points. The size of the black dots shows the sample size with which the mean was calculated. Note also the clever use of gray to give visual preference to the (more convincing) black dots.

Reference Webb, T.J., Gaston, K.J., Hannah, L. and Woodward, F.I. (2006) Coincident scales of forest feedback on climate and conservation in a diversity hot spot. Proceedings of the Royal Society B: Biological Sciences 273: 757-765. (download free pdf from journal website)