Google Maps and GHCN

This page shows in a Google maps framework the 7280 stations of the GHCN Monthly network. To the side is a panel where you can choose which stations will be shown, and with what colors. You can select by metadata like altitude or urban status, or by ranges of data. here the data is a variety of trend options over the last 30, 50 or 60 years. The options are trends from the GHCN unadjusted data file, or adjusted, or the difference if you want to see what effect adjustment had.

I'll explain methods below the gadget.



The initial display shows an arbitrary selection. It has available all the usual Google Maps facilities, with controls at top left. But particularly you can click on any marker to bring up a balloon of information. This includes name, a link to the NOAA data sheet attached to the GHCN number, some metadata, and a trend number.

At the bottom of the box on the right, there is a selection box which determines that trend type. It has combinations of Unadj, Adj and A-U, meaning GHCN trend of unadjusted, adjusted and the trend difference. Choosing there determines what is meant by "Trend" elsewhere.

The green box on the right has a collection of selection criteria. Some are comparisons, some are logical. The second small button toggles between the relation options (>,==,T/F etc), and for comparison, the third is a text box in which you enter the reference value. Only one selection can be live at a time, determined by the left radio button. If nothing is live, nothing happens.

When you have a live selection, you can click a radio button in the top orange section (Pink,Cyan etc). Any stations that fulfill your requirement will change to that color. In the middle column, the numbers in each color are shown, and updated with each choice. Invisibles are still in the totals. This is a very handy way of displaying a count of a subset.

The right column shows the most recent logical operation that was implemented for that color. It's just a reminder and does not show the status of all markers in that color. If the color is eg pink, then the expression will not include markers that were pink before the latest selection, and the other logicals don't change.

The All button, when F does nothing, but when T and live changes everything to one color. You may want to start with everything invisible. I'd make this the default, except that it is a bit discouraging when the screen first comes up.

You can enter NaN into the text fields, which will have the effect of changing any NaN to that color. Usually used to make them invisible. For Trend_Adj, there is the option of equality ("=="), mainly used to test for zero. I should warn that it tests to rounding level, which is 0.01. Very few stations totally escape adjustment (eg MMTS), but it is often very small.

I've included Lat and Lon; it doesn't mean much when you have a map. but is useful for counting, eg Arctic. I have given Urban and Rural as separate options, because there is also Mixed. So if you color Urban T, that is what you see, but Rural F gives Urban and Mixed.

You'll find negative logic useful. The advice on how to sculpt an elephant is, take a very big rock and chip away anything that doesn't look like an elephant. Same here. If you want pink to show urban stations that have trend increased on adjustment, then pink all uptrended, then go to Urban F, and make that invisible. That will affect other colors too (if any).

Earlier Google maps posts include:




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