Free GIS – GENeSIS

March 6, 2011

A Week in the Life of a Tile Server

Recently, BBC Look East have been running a “Broadband Speed Survey”, asking people to use an online tester to check their broadband speed, and then enter the value, along with their postcode, into SurveyMapper. This generated 16,311 responses to the survey, but for each response people get to view the map containing the latest data, so the tile server drawing the data on the map gets about 100 times as many hits.

When the survey was advertised on the 18:30 news bulletin on the Tuesday that week, we started to get a huge number of hits in a very short space of time. The following graph shows the hits by hour of day for all five days that week.

The peaks tie in quite well with the 18:30 and 22:30 news bulletins, but it can be seen from the statistics that the tile server took over a million hits in the space of a couple of hours. The tile server itself is a single machine running Server 2008 R2 Core, virtualised with two processors assigned. Once it became apparent how many hits we were getting, this was increased to 4 processors and 4GB of RAM. This shows the main benefit of virtualisation for us, which is that we could shutdown non-operational machines used purely for research and divert the computing power to the operational web servers which were taking the high loads. In order for the maps on SurveyMapper to work, we are also dependent on a database server and the dedicated web server which runs the MapTube and SurveyMapper sites, in additional to the tile server. What’s interesting about this experience is that it taught us that the database server is capable of handling a much higher load than this.

From the graph of the daily hits, it can be seen that most of the traffic was on Tuesday 22nd February, which is the first day it was advertised on the news. After this it tails off as the week progresses. One other interesting thing that was noticed when analysing the log files is the browser and operating system statistics.

So, from these statistics, it’s a three way split between Windows XP, Vista and 7, with IE8 the most popular browser. Chrome, Firefox and Safari are lagging behind, which is surprising bearing in mind the profileration of Macs.

Now that we’ve proved a single element IIS7.5 server can take a million hits, we’re looking into the possibility of creating multiple tile servers dsitributed across two virtualisation servers and load balancing.

August 4, 2010

MapTube Clickable Maps

We’ve just updated the MapTube website with a new release of the software that makes all of the Census maps clickable. Anything tagged with the “CENSUS2001″ keyword is clickable, as well as most of the maps made from the data on the London DataStore.

The new clickable map icon. This is used to turn the clickable maps feature on or off.

The resulting popup window showing attribute data for the feature that has been clicked.

The maps page now contains an additional button below the zoom level slider which shows a representation of a mouse. If this is enabled, as shown below, then a single mouse click on the map will display a popup window containing more information about the feature just as in a traditional GIS.

The image on the right shows the default popup window which just lists the attributes from the CSV file used to make the map. If you want to examine the data, there is a link to download the CSV file from the ‘more information’ page.

The html in the popup window is obtained by applying a transformation to the attribute data that turns it into the html that you see displayed in the window. In the next release of MapTube we will include a user interface to allow people to build maps of fixed geometry data (i.e. census data, ward codes, districts, countries etc) directly from data in a CSV file. We are also planning to add a web based interface to allow people to write what appears in the popup window themselves so that it will be possible to include graphs and charts.

May 13, 2010

UK General Election 2010: Results

With 649 of the 650 parliamentary seats from the 6th May 2010 General Election now declared, we can see how the policital map of the UK has changed. The one remaining seat is Thirsk and Malton where the death of one of the candidates means that the vote has been postponed until 25th May.

Election 2010 Result Political Party Colours

This map has been uploaded to our MapTube website so that the results can be compared with some of our other maps.

Here are some interesting comparisons:

Compare the 2005 election to the 2010 election results:

http://www.maptube.org/election/map.aspx?s=DGxUoiNcsKkGNyyDLBwcCnOMChZsgZwcHApzPApTnd

The 2010 result is shown on the top layer, so move the red slider left and right to see how the political outlook has changed between 2005 and 2010. Apologies for the change in the SNP colour between the two colour scales, but I will upload a new one with standardised colours later. Also, Northern Ireland is missing as we don’t have a boundary dataset for this country, but we are currently trying to obtain one.

Did the MPs’ expenses scandal cause existing MPs to lose their seats?

http://www.maptube.org/election/map.aspx?s=DGxUoiNcsKkGNyyBPAwMCnOcCidsgywcHApzfAoWbd

The top layer shows the parliamentary constituencies where MPs have been told to pay back expenses according to the Sir Thomas Legg report. Slide the top layer slider left and right to see where the parties have changed. This only shows the party colours and not how much MPs were asked to pay back. The result is actually rather inconclusive. Where there are changes, it’s possibly as much a result of boundary changes as expenses repayments. What is required is a comparison that takes both the boundary changes and repayment amounts into account.

Once the final election analysis is available we will add a 2010 turnout map and proportional representation maps of the main parties showing what percentage of the electorate voted for each party by constituency.

May 20, 2009

From Tile Pyramids to Population Pyramids

It’s actually a stacked bar chart rather than a traditional population pyramid, but the image below shows male/female population by age for all the output areas in England. The red thematic overlay is total population for every OA, which can be clicked to get the age group breakdown shown in the popup window.

This map is a variation on the original clickable OAC map and was built using a new version of the GMapCreator which contains the clickable technology. Traditionally, maps like this have been built using a server and database to translate the click on the client into a geographic area using point in polygon and then sending the query data back to the client. This method doesn’t scale when you have limited server resources and are looking to handle high numbers of hits, for example with the Mood Maps that we’ve been doing recently. An alternative solution is to build feature coded tiles and let the client handle most of the work displaying the data. Using this system, there is a second set of tiles, one of which the client downloads when the user clicks on a point. This allows the client to work out which feature has been clicked and request the data for that area as an xml file.

The hard part is designing a system which can allow people to design the popup window without having to resort to programming. In the example above, the graph was created using Google Charts via the GMapCreator’s user interface. All that was needed was to choose the data fields from a list and to select the chart type. The URI string to create the chart comes from an xslt transform applied to the xml data. This transform is automatically created by the GMapCreator interface, which also allows the rest of the popup window to be designed using a simple html editor.