Abstract
BackgroundSelf-organizing maps (SOMs) have now been applied for a number of years to identify patterns in large datasets; yet, their application in the spatiotemporal domain has been lagging. Here, we demonstrate how spatialtemporal disease diffusion patterns can be analysed using SOMs and Sammon’s projection.MethodsSOMs were applied to identify synchrony between spatial locations, to group epidemic waves based on similarity of diffusion pattern and to construct sequence of maps of synoptic states. The Sammon’s projection was used to created diffusion trajectories from the SOM output. These methods were demonstrated with a dataset that reports Measles outbreaks that took place in Iceland in the period 1946–1970. The dataset reports the number of Measles cases per month in 50 medical districts.ResultsBoth stable and incidental synchronisation between medical districts were identified as well as two distinct groups of epidemic waves, a uniformly structured fast developing group and a multiform slow developing group. Diffusion trajectories for the fast developing group indicate a typical diffusion pattern from Reykjavik to the northern and eastern parts of the island. For the other group, diffusion trajectories are heterogeneous, deviating from the Reykjavik pattern.ConclusionsThis study demonstrates the applicability of SOMs (combined with Sammon’s Projection and GIS) in spatiotemporal diffusion analyses. It shows how to visualise diffusion patterns to identify (dis)similarity between individual waves and between individual waves and an overall time-series performing integrated analysis of synchrony and diffusion trajectories.
Highlights
Self-organizing maps (SOMs) have been applied for a number of years to identify patterns in large datasets; yet, their application in the spatiotemporal domain has been lagging
Spatiotemporal analysis of epidemic waves can reveal important information on anomalies and trends, and provide inside into the underlying diffusion patterns [1,2]. These patterns are categorised as contagious spread, hierarchical spread, or mixed diffusion
When visualising the component planes of this class (Figure 6 – cluster 5), it turns out that the patterns in this group are not very prominent and the group is not very homogeneous compared to the other classes
Summary
Self-organizing maps (SOMs) have been applied for a number of years to identify patterns in large datasets; yet, their application in the spatiotemporal domain has been lagging. Spatiotemporal analysis of epidemic waves can reveal important information on anomalies and trends, and provide inside into the underlying diffusion patterns [1,2]. These patterns are categorised as contagious spread, hierarchical spread, or mixed diffusion. Hierarchical spread refers to disease transmission through an ordered sequence of geographic locations (normally based on their size) [1] and it can be related to the movement of people, carrying a disease to a new centre of population via long distance travel. Hierarchical spread is typically characterized by the display of synchrony among locations that have similar size but that are geographically apart [2].
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