Tuesday, 17 August 2010

Visualizing the Global Population Dynamics Database

The Global Population Dynamics Database (GPDD) is comprised of over 5000 long-term species abundance time series, over 270,000 spatiotemporally referenced data points in all. How can these data be visualized to explore spatiotemporal correlations between series?

The data is four dimensional: latitude, longitude, time and abundance. The geographical coordinates are all in decimal degrees so compatible across series. Series differ in temporal resolution and coverage, as well in their units of abundance.

Dates were converted to decimal years by adding the proportion of the year the observation was taken at to the year. For example, 0.04167 was added to 'January' abundances: (month number * 1/12) + 1/24.

Log abundance series were untransformed, and then all standardized (SS) by subtracting mean and dividing by the variance.

Here are two fly-by animations of these data, both done in ArcScene:

2903 european series (131,000 observations) as line-plots offset in longitude by 6 * SS (above the mean to the east, below to the west). Series are coloured by species and displayed against annual mean temperature in 1900, 1921, 1941, 1961, 1981 and 2001. This approach shows the overall distribution of series but little other pattern is revealed without interactive manipulation.

Abundance of Lynx (L. lynx , L. canadensis & L. rufus), with spheres proportional to SS. Note the pronounced and highly spatially and temporally correlated population cycles in L. canadensis compared to L. rufus.

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