Fig. 2
From: A topological data analysis based classification method for multiple measurements
Schematics of the Mapper construction. Filter function f maps datapoints to intervals of real numbers. Those points mapping to the same interval constitute a cluster under the filtering by f and corresponding nodes in the Mapper graph. This is indicated, respectively, by blue, red and green intervals and corresponding blue, red and green nodes below. When two intervals overlap and they have datapoints in common, the corresponding nodes in the Mapper graph are connected by an edge. This happens for blue and red nodes but the datapoints in the green node are an isolated cluster