Petition platforms, where citizens may create and sign petitions to the government or legislature, have been adopted in many liberal democracies, including the US, the UK and Germany. These platforms can be mined to generate ‘big data’ on petition signing which provides new insight into the ecology of this form of political participation, data of a kind rarely seen in political science. This paper visualizes and models such data for all petitions created on the UK government petition platform over a three year period (including a comparison with similar data for the US); illustrates the effect on petition signing of a platform change to provide social information in the form of trending petitions; and shows how the analysis of such data might be used to inform policy change and platform redesign.