I have been updating my weather site lately and have included charts to display data for each month. I decided to use the free Google chart API for most of the charts since they are easy and quite cool.
For those who have not seen the Google Chart API see - http://code.google.com/apis/chart/
Here are some live examples of what you can do with the chart API
http://chart.apis.google.com/chart?cht=p3&chd=t:60,40&chs=250x100&chl=Hello|World
http://chart.apis.google.com/chart?cht=p3&chs=220x100&chd=s:Hellob&chl=May|Jun|Jul|Aug|Sep|Oct
http://chart.apis.google.com/chart?cht=lc&chd=s:pqokeYONOMEBAKPOQVTXZdecaZcglprqxuux393ztpoonkeggjp&chco=676767&chls=4.0,3.0,0.0&
chs=200x125&chxt=x,y&chxl=0:|1|2|3|4|5|1:|0|50|100&chf=c,lg,0,76A4FB,1,ffffff,0|bg,s,EFEFEF
Right enough of the Google API - go check it out at - http://code.google.com/apis/chart/
Now I do not know what type of chart you call the one I wrote in c# (with the help of Simeon - see http://simeonpilgrim.com/blog/2008/09/08/timedirection-graph/) but here is an example showing the Wind direction over the month. The inner portion of the chart is the oldest data and the outer area is the newest data.
The chart above is made with 744 data points, 1 per hour over the period of the month of August 2008.
At this point I will probably refine it a bit more but I will release the source when I am happy with it.
To see more of these charts in action look at http://weather.crowe.co.nz/Charts.aspx