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Posted by on Mar 30, 2012 in Featured Maps, R Spatial, Slideshow, Visualisation | 22 comments

Mapped: British, Spanish and Dutch Shipping 1750-1800

Mapped: British, Spanish and Dutch Shipping 1750-1800

I recently stumbled upon a fascinating dataset which contains digitised information from the log books of ships (mostly from Britain, France, Spain and The Netherlands) sailing between 1750 and 1850. The creation of this dataset was completed as part of the Climatological Database for the World’s Oceans 1750-1850 (CLIWOC) project. The routes are plotted from the lat/long positions derived from the ships’ logs. I have played around with the original data a little to clean it up (I removed routes where there was a gap of over 1000km between known points, and only mapped to the year 1800). As you can see the British (above) and Spanish and Dutch (below) had very different trading priorities over this period. What fascinates me most about these maps is the thousands (if not millions) of man hours required to create them. Today we churn out digital spatial information all the time without thinking, but for each set of coordinates contained in these maps a ship and her crew had to sail there and someone had...

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Posted by on Sep 8, 2010 in R Spatial, Resources | 6 comments

Clipping a Surface By a Polygon

Clipping a Surface By a Polygon

Background: A common function in standard GIS software enables users to create a raster surface and extract values or clip it based on a set of polygons. This may be used in cases where you want analysis to be constrained to within a town’s boundaries or a coastline. This tutorial will outline how to create a surface using kernel density estimation (KDE) and then clip the surface so that it is constrained within the City of London Boundary. Data Requirements: City of London Boundary Shapefile: Download (requires unzipping). London Cycle Hire Locations: Download. Install the following packages (if you haven’t done so already): sm, maptools.? Click here to view the...

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Posted by on Sep 7, 2010 in R Spatial, Resources | 2 comments

Writing a Spatial Function: The Location Quotient

Background: In some cases it is necessary to conduct the same analysis multiple times on either the same or different data. In such circumstances it is worth writing a function to simplify the code. In this example the location quotient provides a simple calculation easily written in to a function. The location quotient (LQ) is an index for comparing a region’s share of a particular activity with the share of that same activity found at a more aggregate spatial level (a good book on this kind of thing is Burt et al.). In this example we take a shapefile of London Boroughs that contains information on the population of each borough and the percentage of sports participation in each borough. In this case there is little point in calculating the LQ as the percentage alone would be more meaningful. The focus here is how to undertake the methods, not their appropriate use, or the validity of the results. Data Requirements: London Sport Participation Shapefile: Download (requires unzipping) Install the...

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Posted by on Sep 6, 2010 in R Spatial, Resources | 6 comments

R Maps

R Maps

This is an updated version of my Making Maps with R tutorial. I think the code is lot simpler and it also includes some data for you to play around with. Background: Spatial data are becoming increasingly common, as are the tools available in R to process it. Of course one of the best ways of visualizing spatial data is through a map. Maps need to be well thought out. Not least, the selected colours need to be appropriate and sufficient context is provided through the use of a legend, title, scale bar and north arrow. The worksheet will demonstrate how to produce a map with R that includes all these elements. Data Requirements: London Sport Participation Shapefile. Download (requires unzipping) Install the following packages (if you haven’t already done so): maptools, RColorBrewer, classInt Click here to view the tutorial...

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