I thought I'd try something a little more sophisticated this morning with the snowfall data.
So I took all the data I got from the NOAA site for all weather reporting sites (in their list), extracted just the data for cities in New York, between Nov 2 and Nov 22. I dumped this into a table like this:
This is pretty much just copy/pasted from their CSV file into my text editor.
A small, but important point to notice here. I wanted the first column ("Location") to be a comma-separated Lat/Long pair. The easiest way to convert from a CSV file (where Lat and Long were in different columns) into a TSV file was to import everything into a spreadsheet, then write a small converter function that would concatenate the Lat + "," + Long into a single cell. Then, save everything as a TAB-separated file (TSV). That makes column one into a handy lat/long pair (like the first one: 42.74, -73.81 is the lat/long for Albany NY). I also wrote an sum column at the end (that is, =SUM(A2:A26) which would add up all the snowfalls for the entire period), so the last column is total snowfall.
Once I have this file, I can create a map of the total snowfall.
I did the obvious search:
[ heat map tool ]
and found the OpenHeatMap site. It's really very easy to use--just upload your data, and you can make this map (showing the location of each of the snowfall summary rows, distributed on the map by the lat/long in column 1).
|Figure 1. A choropleth map of NY state cumulative snowfall, first 2 weeks of November, 2014. Data from NOAA.|
Strictly speaking, this is NOT a heat map (they admit as much on their website). A heat map is a visualization of a matrix where each point in the array is color-coded.
This figure above is actually a choropleth map. Say that 5 times fast to get it firmly lodged in your brain. Here's the difference: A heat map is a colorized regular grid. A choropleth map is a colorized symbol (like the circles above) or a symbolic element (such as a state in a colored state map) where the size or color indicate the variable value.
In Figure 1 above, the circles vary in both size and color--that makes it a choropleth map. When you click on one of the circles, you can see the value of that location. Example:
BUT... One of the options in OpenHeatMap is to blur/fuzz the circles. This operation makes it LOOK like a heat map, but it's really just a fuzzy choropleth. You have to be careful not to overinterpret what you're seeing. The snow doesn't magically smoothly fall off the way this chart suggests. Remember that ALL the data we have is total snowfall for a particular point. This kind of chart suggests much more than is really here.
|Figure 2. The same map as in Figure 1, just blurred a bit and using a rainbow from blue-to-red coloring scheme.|
|Figure 3. A Fusion Table view of the same data.|
There you go, a slightly more sophisticated version of the snowfall map.
If anyone is up for a Challenge over the Thanksgiving holiday, try this: Can you make an animated version of the snowfall chart? That is, could you make something like this?
If so, Search On!