Two-point Equidistant Projection and Degree-of-interest Filtering for Smooth Exploration of Geo-referenced Networks

TL;DR

Geo-referenced networks with uneven node distributions challenge spatial understanding during navigation. The authors propose an ego-perspective visualization with a central map, edge proxies, and animated zoom-and-pan transitions, leveraging Mercator and two-point equidistant projections (tpeqd/azeqd) together with degree-of-interest (DoI) filtering. A proxy-based DoI-driven approach and projection-aware transitions are introduced, with an online study comparing projection types for directional comprehension. The work aims to enable more space-efficient exploration of geo-referenced graphs while preserving scale, direction, and context, with potential for domain-specific DoI customization.

Abstract

The visualization and interactive exploration of geo-referenced networks poses challenges if the network's nodes are not evenly distributed. Our approach proposes new ways of realizing animated transitions for exploring such networks from an ego-perspective. We aim to reduce the required screen estate while maintaining the viewers' mental map of distances and directions. A preliminary study provides first insights of the comprehensiveness of animated geographic transitions regarding directional relationships between start and end point in different projections. Two use cases showcase how ego-perspective graph exploration can be supported using less screen space than previous approaches.

Figures (3)

• Figure 1: Our initial prototype showed maps in Mercator projection. On-screen vertices are connected explicitly. Proxies to off-screen vertices are shown at the edge, and aggregated as needed. Various DoI functions can be combined with different weights for a total DoI function that decides which vertices to show.
• Figure 2: Example stimuli frames (a) for the tpeqd projection (top) and Mercator projection (bottom). The first half, until the point where both locations are visible, of two animated transitions are shown. The participants then had to specify the direction from the start point to the end point on the transition on an empty globe (b).
• Figure 3: CI of the pairwise differences between the three projections, with Bonferroni correction (factor of 9) indicated by red whiskers. The CI are calculated for the absolute error in angle of the direction task, and for the active time. For the error differences involving tpeqd, the estimation of the corrected error when rotating the projection such that north is up for the start point (see discussion at the end of \ref{['sec:evaluation']}) is plotted in blue.