Spatial Analysis » Software

Great Maps with ggplot2

James — Thu, 02 Feb 2012 13:02:15 +0000

The above map (and this one) was produced using R and ggplot2 and serve to demonstrate just how sophisticated R visualisations can be. We are used to seeing similar maps produced with conventional GIS platforms or software such as Processing but I hadn’t yet seen one from the R community (feel free to suggest some in the comments). The map contains three layers: buildings, water and the journey segments. The most challenging aspect was to change the standard line ends in geom_segment from “butt” to “round” in order that the lines appeared continuous and not with “cracks” in, see below.

I am grateful to Hadley and the rest of the ggplot2 Google Group for the solution. You can see it here. From this point I layered the plots using the geom_polygon() command for the buildings and water bodies and my new function geom_segment2() for the journey segments- these were simply the start and end latitudes and longitudes for each node in the road network and the number of times a cyclist passed between them. I have included the code below

#Code supplied by james cheshire Feb 2012 #load packages and enter development mode library('devtools') dev_mode() library(ggplot2) library(proto)


#if your map data is a shapefile use maptools

library(maptools)

gpclibPermit()
#create GeomSegment2 function

GeomSegment2 <- proto(ggplot2:::GeomSegment, {

 objname <- "geom_segment2"

 draw <- function(., data, scales, coordinates, arrow=NULL, ...) {

  if (is.linear(coordinates)) {

    return(with(coord_transform(coordinates, data, scales),

      segmentsGrob(x, y, xend, yend, default.units="native",

      gp = gpar(col=alpha(colour, alpha), lwd=size * .pt,

        lty=linetype, lineend = "round"),

      arrow = arrow)

    ))

  }

}})
geom_segment2 <- function(mapping = NULL, data = NULL, stat =

"identity", position = "identity", arrow = NULL, ...)  {

 GeomSegment2$new(mapping = mapping, data = data, stat = stat,

       position = position, arrow = arrow, ...)

}
#load data stlat/stlong are the start points elat/elong are the end points of the lines

lon<- read.csv("bikes_london.csv", header=F, sep=";")

names(lon)<-c("stlat", "stlon", "elat", "elong", "count")
#load spatial data. You need to fortify if loaded as a shapefile

water<- fortify(readShapePoly("waterfeatures.shp"))

built<- fortify(readShapePoly("buildings.shp"))
#This step removes the axes labels etc when called in the plot.

xquiet<- scale_x_continuous("", breaks=NA)

yquiet<-scale_y_continuous("", breaks=NA)

quiet<-list(xquiet, yquiet)
#create base plot

plon1<- ggplot(lon, aes(x=stlon, y=stlat))
#ready the plot layers

pbuilt<-c(geom_polygon(data=built, aes(x=long, y=lat, group=group), colour= "#4B4B4B", fill="#4F4F4F", lwd=0.2))

pwater<-c(geom_polygon(data=water, aes(x=long, y=lat, group=group), colour= "#708090", fill="#708090"))
#create plot

plon2<- plon1 +pbuilt+ pwater+ geom_segment2(aes(xend=elong, yend=elat, size= count, colour=count))+scale_size(range=c(0.06, 1.8))+scale_colour_gradient(low="#FFFFFF", high="#FFFF33", space="rgb")+coord_equal(ratio=1/cos(lon$elat[1]*pi/180))+quiet+ opts(panel.background=theme_rect(fill="#404040"))

plon2

Automated Cartography: The urban expansion of Lansing

James — Mon, 28 Feb 2011 12:10:07 +0000

I hadn’t seen this video before. It demonstrates one of the earliest attempts at automated cartography for the display of time with spatial data. Truly ground breaking, the video shows the urban growth of Lansing at 5 yearly intervals from between 1850 and 1965 and was produced by Allan Schmidt at the Michigan State University Urban Regional Research Institute. The visualisation was produced with the synergraphic mapping system (SYMAP) developed by Howard Fisher in the mid 1960s. More details and a fully downloadable version can be found here. A presentation on SYMAP is available here. The sequence starts with a slow version of two minutes forty-five seconds before repeating the sequence more rapidly in forty-five seconds, and finally in five seconds.

ESRI (UK) Case Study

James — Tue, 22 Feb 2011 10:13:00 +0000

Buried deep in the ESRI (UK) website is a case study I helped put together showcasing some of the ways we use GIS (specifically ESRI products) within UCL Department of Geography and Centre for Advanced Spatial Analysis. ESRI (UK) co-sponsor my PhD research and I have had a very positive and productive relationship with the company. I know that they are keen to promote the use of their software within higher-education (and at secondary schools) and you can find out more here. Click on the image below for the case study.

Installing rgdal on Mac OS X

James — Tue, 02 Nov 2010 17:43:06 +0000

******Roger Bivand has kindly just emailed me to say:

“Your 2 November blog about rgdal on OSX is very misleading. The CRAN rgdal page: http://cran.r-project.org/web/packages/rgdal/index.html says all you need to know unless you need extra drivers, or already have PROJ.4 and GDAL installed. Just do:

setRepositories(ind=1:2)
install.packages(“rgdal”)

installs rgdal with all its external dependencies satisfied. It is kindly provided by Prof. Brian Ripley, and is presently running up-to-date GDAL.”******

This may offer a straightforward solution. I would be interested to hear how people get on.

After running a spatial data analysis with R session today, it became apparent that there are one or two teething problems installing the important rgdal package on Mac OS X operating systems. The usual install.packages(“rgdal”) won’t work. My colleague Jon Reades did some digging around to find this solution. I have tested it and it seems to work fine.

[Note that you'll need to be comfortable with the Terminal. If you're not, then find someone who is.]

1. Download the GDAL OS X install from kyngchaos
- http://www.kyngchaos.com/files/software/unixport/GDAL_Complete-1.7.dmg
(Looks like the basic page [for updates after 1.7 if you're reading this ages from now] is http://www.kyngchaos.com/software/frameworks)
- Install as per usual OS X install system
- Fire up the Terminal, then pico (or vi[m]) the .bash_login file
- Modify the PATH environment so that it reads:
export PATH=”/Library/Frameworks/GDAL.framework/Programs:$PATH”
[This is what enables the subsequent steps to find gdal-config]

2. Download and install proj4 from source
- http://trac.osgeo.org/proj/wiki/WikiStart#Download
- Download source code version proj-4.7.0.tar.gz
- Fire up the Terminal
> cd ~/Downloads/
> tar -xzvf proj-4.7.0.tar.gz
> cd proj-4.7.0
> ./configure
> make && make test
> sudo make install
[ should install to /usr/local/lib by default]

3. Download and install rgdal from source
- http://cran.r-project.org/src/contrib/rgdal_0.6-28.tar.gz
- Fire up the Terminal
> cd ~/Downloads/
> sudo R CMD INSTALL –configure-args=’–with-proj-include=/usr/local/lib’ rgdal_0.6-28.tar.gz

After all of this mucking about I was able to say:

> require(sp)
> require(rgdal)

And get a message indicating that GDAL was loaded successfully.

He also posted his solution on the Computational Mathematics Blog. If there is a better way I would be interested in hearing about it for future classes.

Surname Diversity in Great Britain

James — Fri, 20 Aug 2010 09:28:47 +0000

As part of my PhD research I recently produced the map below (high res. version) that shows the diversity of surnames in Great Britain. I wanted to demonstrate that surname diversity is not uniform across Great Britain. For example towns and cities (especially London) have relatively high surname diversities compared with rural areas because more migrants and single people live in them. Wales has a very low surname diversity due to its past naming conventions. The measure used is calculated by dividing the number of surnames by the total population of each Output Area (OA). There are over 200,000 OAs in Britain. Urban OAs are very small despite accounting for a large proportion of the total population, so I have scaled the size of each OA by their population (the map is therefore a cartogram). This creates the somewhat bloated appearance of Great Britain, but serves to emphasise the increased surname diversity (due to more single people and migrants) in towns and cities. The correct shape of Great Britain is shown in the inset. For more technical info please see below.

To create this map I used ArcGIS 10 and the Cartogram Geoprocessing Tool. The nice thing about the tool is that it is not dependent on VBA and therefore worked straight off in ArcGIS 10. There are over 220,000 spatial units in this map and the tool had no problems processing them. I have not found any alternatives that work for this volume of data.

ArcGIS for iPhone: Review

James — Mon, 19 Jul 2010 14:27:12 +0000

ESRI have just launched their ArcGIS for iPhone Application. I have tested it out and thought I would share a my first impressions. I conducted the test on my iPhone 3GS running software version 4.0.1 and with 1 to 3 bars of 3G signal.

Overall I found the app to be very impressive. You are greeted with a world map that you can instantly interact with by panning and zooming in the usual way.

The map tiles loaded surprisingly quickly- it took approx 5 seconds to zoom from the above view to building level with only 1 bar of signal.

Users can search for places of interest…

…but this provided the only disappointment with the map appearing to lack the required data.

Zooming out a little resolved this problem, but I am not sure how many people would think to do this. I suspect the problem is relatively easily addressed and may well be in future updates. Offering standard maps is not particularly innovative and not what the app sets out to achieve. The real innovation is the ability to view layers available from the ArcGIS.com website. You can, for example, use OpenStreetMap as the base map

or overlay additional information, in this case the Gulf Oil Spill Forecast:

Navigation to layers is straightforward:

I especially like the fact that users can add their own servers and also bookmark their favourite layers. On top of these features users can measure distances and calculate areas.

I found these tools to be extremely intuitive and I expect they will become an integral part to many field based introductory GIS courses. In a recent talk I attended, Jack Dangermond said that GIS software in the past was made to be complicated. With this application ESRI have demonstrated that GIS can be made to be easy. I think all who use this app both from within and beyond GIS with be genuinely impressed.

**I have just discovered a more in depth review worth reading from James Fee’s GIS blog.**

Top 60 Chinese Cities

James — Mon, 07 Jun 2010 10:19:58 +0000

Cities are one of the many phenomena that follow a long-tailed distribution. In simple terms there are a few big cities and lots of small ones. The classic way of showing a long tailed distribution (and the method from which the name is taken) is to produce as plot such as that below:

The infographic at the top of the post by chinfographics.com demonstrates the distribution in a more engaging and constructive way.

One method I have used in the past to demonstrate data with a long tailed distribution is the excellent Wordle tool. I have created a Wordle (below) for the same data (downloaded from Chinfographics). Whilst it does not compete with the Chinfographics infographic in terms of quality, I still think Wordles provide a very simple, and effective, method of displaying data with a “long tail”.

Graduate Jobs with ESRI (UK)

James — Mon, 26 Apr 2010 10:43:18 +0000

ESRI (UK) have a couple of graduate vacancies with their Technical Solutions Group (TSG) for the following roles:

GIS Developer:

Reporting to the TSG Technology Manager, the role of the GIS Developer is to support the sales process through the development of bespoke demonstration applications, and to work with Customers and Business Partner organisations to provide technical advice and guidance. The role requires the individual to be both analytical and Customer facing, therefore experience of working in a Customer facing environment and confidence at presenting to an audience is essential. Ideally the individual will be educated to degree level or above in a Computer Science, Software Engineering or an IT related subject

Ideally the individual will be educated to degree level or above in GIS or an IT related subject.

This role would suit a graduate with at least 1 years post graduate experience.

If you are interested in exploring the above opportunity in more depth, please email (preferably) or write to us, enclosing your CV and details of your availability (both for interview and for job commencement, if successful) and your current and expected salary.

GIS Consultant

Reporting to the TSG Industry Manager, the GIS Consultant is responsible for providing Technical Input (including demonstrations and presentations) to support Customer meetings and other sales / marketing activities. The role requires the individual to be both analytical and Customer facing, therefore experience of working in a Customer facing environment and confidence at presenting to an audience is essential.

Ideally the individual will be educated to degree level or above in GIS or an IT related subject.

This role would suit a graduate with at least 1 years post graduate experience.

Applications should be marked ‘Private and confidential’ and submitted to:

HR Department (Email:hrteam@esriuk.com)

ESRI (UK) Ltd, Millennium House, 65 Walton Street, Aylesbury HP21 7QG
Telephone: 01296 745 500

Closing date: 7th May 2010

Jack Dangermond at Where 2.0: GIS on the Web–A Big Step

James — Sat, 03 Apr 2010 07:43:34 +0000

I have embedded below Jack Dangermond’s recent talk at Where 2.0. It introduces the exciting opportunities provided by what Dangermond calls “GIS in the Sky”. Thanks to Alex Singleton for sending me the link to the video posted on GIS and Science.

Mapping and Colour blindness

James — Wed, 10 Mar 2010 15:28:18 +0000

The explosion in spatial data availability and dissemination through online visualisation has produced many interesting maps. A friend of mine, however, recently commented that not enough is done for those with colour blindess. To see the impact of this I was recommended a great website developed by Stanford University that enables users to check how clear their images are to colour blind people. I have run this test for a number of maps below. The top three maps are amongst the most popular maps on CASA’s Maptube Website whilst the fourth map is one of my own. The top two are have undergone the test for Deuteranope colour blindness and the bottom two for Protanope colour blindness.

I was amazed at how indistinguishable seemingly contrasting colours can be. The final map fares best and I think this is because it is simply differing shades of the same colour. If I am honest colour blindness is not something I have seriously considered in my own maps until now so I cannot claim to be a good example. From now on, however, I intend to make a real effort in colour selection for my maps. You can’t go far wrong with the Colorbrewer palettes so I will make the effort to use these as much as possible in the future.

Thanks to Jess Wardlaw for telling me about Vischeck.