I realize I actually know very little about the political process in China
are there regular elections there? what are they voting on? I perceive that you're not voting for any politicians from opposition parties to the official communist party, am I wrong? are you voting on who gets to control the party apparatus within the communist party? who is that vote actually open to?
I also can't tell if the map is supposed to illustrate turnout as a percentage or as an absolute number. The wording ("Territory size shows the estimated proportion of all people who voted in elections between 1945 and 1998 who voted there.") suggests the former, but the actual sizes on the map appear to be the latter, which makes it nearly indistinguishable from the population cartogram: http://worldmapper.org/display.php?selected=2
So imagine you vote for town council. The town councils in your county elect a county council, the county councils elect a state legislature, and the state legislatures elect Congress.
Elections for local people's congress are - for China - fairly open. There are 50-100% more candidates than seats. But candidates are in practice only nominated by the CP and related organizations. But the point is, you can choose between a couple of alternative CP picks, rather than having a single CP pick imposed upon you. A little bit like elections in Iran, I guess. That's not wide open elections like in the West, but it's not nothing.
Elections are more centrally controlled the higher up in the hierarchy you go, but there is always some wiggle room.
There's more than a billion people in China. If 10% of them turn out to vote, then that's already more than the turnout for the 2016 presidential election.