1. A computer implemented method of smoothing transitions between image data displayed at discrete time steps, comprising: receiving, by one or more processors, images defining frames appearing at discrete respective time steps in an animated sequence, including receiving a first image and a second image defining consecutive image frames, wherein the first image frame has a first number of features and the second image has a second number of features, each feature individually representing a building; displaying the images of the animated sequence consecutively at the corresponding discrete time steps, unless, when the second number is greater than the first number at least by a factor of two, smoothing distribution of the features by: computing, by the one or more processors, fractional time steps between the first discrete time step and the second discrete time step to modify the animated sequence, determining, by the one or more processors, features at the fractional time steps, including interpolating a number of features between the first number and the second number to generate a larger number of features at each time step in the sequence relative to a previous time step in the sequence; and generating, by the one or more processors, respective frames for each of the computed fractional time steps, each of the frames including the corresponding determined features.