Friday, December 14, 2012

Universal station locator and history plotter

This is next in the series of things that can be done with XMLHTTPRequest. It merges the capability of the Google Maps display of stations with the machinery of the climate plotter. But the key new thing is that the station location information can be backed up with a store of temperature histories, which can be plotted on demand.

So what we have is a map which allows you to choose a category of stations to show with markers. The usual Google Maps interactivity works. You can choose from different data sets - currently there are GHCN, CRUTEM 4 and the new (and beta) ISTI. BEST will be there soon [Update - it's there now]. Mouse over the markers shows the name. But if you click, you not only get station information as before, but a plot of the annual temperatures in the record (for that data set). You can add to the plot, to, say, compare the records of different data sets. Or you can compare GHCN adjusted with unadjusted, or stations at different locations. And you can smooth and regress. There is an information window that shows the numbers.

How to use it - choosing stations

The map controls are in the table bottom right. Families of controls are indicated by background color. The marker buttons in the top row (None, yellow, pink) are the ones that create actions, in line with the current state of the other selection buttons.

The world is divided into regions, because the larger sets (BEST and ISTI) will make everything about the map very slow if everything is shown. I'd suggest beginning by choosing a single region. The region numbering is shown by a small map under the plot space. You should also choose one or more datasets - GHCN is shown by default, but can be unset. Gadj means GHCN adjusted. You'll probably only want one station for each color. BEST is coming, but not there yet.

You can also choose a subset of those stations. You have to unset the All checkbox, and set the checkbox of the choices you want. The inequality buttons toggle.

When you have chosen a color, marker representing your choices will appear. The choice "None" makes them disappear - often useful. Mouseover the markers to see the names, and when you click, detailed information will appear in the frame bottom left, and a curve will be plotted, or added to the plot. A handle for the curve will be added to the section headed.

Managing the plot

The x and y axes are active. You can click on the pink bars to translate. The step is equal to the distance from the green marker in the middle. The blue bars translate too, but with a fixed point, so the scale changes. On the y-axis, the top stays still, and the bottom point translates (and in between proportionately). For the x-axis, it's the right end that stays still.

There is a column of controls headed Prop/value. To use these you set a value on the rightt, select handles of curves that you want to apply the change to on the left, and then click the prop button to make it happen. For regression you choose type and years (all is default). Colors you can choose from the vertical bar between plot and map. The offset is not incremental - it is what it shows.

There are more usage details on the climate plotter page.


The plot shows annual values. These were taken from the monthly data by averaging (unweighted by days). Missing values were infilled by the monthly average for that station. If more than three months were missing, the year was omitted. I've also omitted sites with less than three eligible years.


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