I'm still new to gravitational lensing, and I've been trying to read a paper that has to do with calculating the week lensing signal of galaxy-galaxy interactions in a sample of galaxies. I understand the equations so far and that the signal is defined by the excess projected surface density $\Delta \Sigma = \Sigma(<r) - \Sigma(r)$, where $r$ is a chosen radius. Then the sample is divided into radial bins of logarithmically increasing $r$, then $\Delta \Sigma$ or $r.\Delta \Sigma$ are plotted versus $r$.
However, I don't really understand the resulting plots where $\Delta \Sigma$ is decreasing, or the variation of $r.\Delta \Sigma$ with $r$.
Any help would be appreciated.