Dr Administrator

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Jun 28 2011

Book review: Map of a Nation by Rachel Hewitt

ordnance“Map of a Nation” by Rachel Hewitt is the story of the Ordnance Survey from its conception following the Jacobite Uprising in Scotland in 1745 to the completion of the First Series maps in 1870. As such it interlinks heavily with previous posts I have made concerning the French meridian survey, Maskelyne’s measurements of the weight of the earth at Schiehallion, Joseph Banks at the Royal Society, William Smith’s geological map of Britain and Gerard Mercator.

The core of the Ordnance Survey’s work was the Triangulation Survey, the construction of a set of triangles across the landscape made by observing the angles between landmarks (or triangulation points) ultimately converted to distances. This process had been invented in the 16th century, however it had been slow to catch on since it was slow and required specialist equipment and knowledge. Chromatic abberration in telescopes was also a factor – if your target is surrounded with multi-colour shadows – which one do you pick to measure? The triangles are large, up to tens of miles along a side, so within these triangles the Interior Survey was made which details the actual features on the ground – tied down by the overarching Triangulation Survey.

A second component of this survey is the baseline measurement – a precise measurement of the length of one side of one triangle made, to put it crudely, by placing rulers end to end over a straight between the terminal triangulation points.

The Triangulation Survey is in contrast to “route” or “transverse” surveys which measure distances along roads by means of a surveyor’s wheel, note significant points along the roadside. There is scope for errors in location to propagate. Some idea of the problem can be gained from this 1734 map showing an overlay of six “pre-triangulation” maps of Scotland, the coastline is all over the place – with discrepancies of 20 miles or so in places.

The motivation for the Ordnance Survey mapping is complex. Its origins were with David Watson in the poorly mapped Scotland of the early part of the 18th century, and the Board of Ordnance – a branch of the military concerned with logistics. There was also a degree of competition with the French, who had completed their triangulation survey for the Carte de Cassini and were in the process of conducting the meridian survey to define the metre. The survey of England and Wales was completed after the Irish Triangulation and after the Great Trigonometric Survey of India – both the result of more pressing military and administrative needs. As the survey developed in England more and more uses were found for it. Indeed late in the process the Poor Law Commission were demanding maps of even higher resolution than those the Ordnance Survey initially proved, in order to provide better sanitation in cities.

The Survey captured popular imagination, the measurements of the baseline at Hounslow Heath were a popular attraction. This quantitative surveying was also in the spirit of the Enlightenment. There was significant involvement of the Royal Society via its president, Joseph Banks, and reports on progress were regularly published through the Society. Over the years after the foundation of the Ordnance Survey in 1791 accurate surveying for canals and railways was to become very important. In the period before the founding of the Ordnance Survey surveying was a skill, related to mathematics, which a gentleman was supposed to possess and perhaps apply to establishing the contents of his estate.

Borda’s repeating circle, used in the French meridian survey to measure angles, found its counterpart in Jesse Ramsden’s “Great Theodolite“, a delicate instrument 3 feet across and weighing 200lbs. The interaction with the French through the surveying of Britain is intriguing. Prior to the French Revolution a joint triangulation survey had been conducted to establish exactly the distance between the Paris and Greenwich meridians, with the two instruments pitted against each other. There was only a 7 foot discrepancy in the 26 miles the two teams measured by triangulation between Dover and Calais. In 1817, less than two years after the Battle of Waterloo a Frenchman, Jean-Baptiste Biot, was in the Shetlands with an English survey team extending the meridian measurements in the United Kingdom.

The accuracy achieved in the survey was impressive, only one baseline measurement is absolutely required to convert the angular distances in the triangulation survey into distances but typically other baselines are measured as a check. The primary baseline for the Triangulation Survey was measured at Hounslow Heath, a second baseline measured at Romney Marsh showed a discrepancy of only 4.5 inches in 28532.92 feet, a further baseline measured at Lough Foyle, in Northern Ireland found a discrepancy of less than 5 inches in 41,640.8873 feet.

The leaders of the Ordnance Survey were somewhat prone to distraction by the terrain they surveyed across, William Roy, for example, wrote on the Roman antiquities of Scotland. Whilst Thomas Colby started on a rather large survey of the life and history of Ireland. Alongside these real distractions were the more practical problems of the naming of places: toponymy, particularly difficult in Wales and Ireland where the surveyors did not share the language of the natives.

Overall a fine book containing a blend of the characters involved in the process, the context of the time, the technical details and an obvious passion for maps.

Footnotes

In writing this blog post I came across some interesting resources:

Jun 28 2011

Universities and knowledge

The Higher Education White Paper is published today, in common with all other commentators in this area I have not read it either. One thing which seems to have attracted comment is the idea that there should be a market in higher education. The academics don’t seem to approve.

But knowledge doesn’t belong to universities. Universities provide qualifications, accreditation, and they provide personalised teaching.

For many students, such as myself 20 years ago, a university education was a given: it was the middle class way of easing myself out of the parental home and the gateway to the career I have now – first as an academic and now as an industrial research scientist. It was available to a relatively small fraction of the population. Things have changed now, increasingly university is seen as the gateway to most careers. Students do not go to university for the love of knowledge, they go because they must to get the careers they want. Pragmatically many careers do not require three years of post-18 education but we are manoeuvring ourselves in to a position where we say they must.

Students will no doubt see themselves in a market – even before this white paper they were being asked to commit significant future income in paying for three years of education, they are foregoing three years of paying work for the promise of a better future. If I were a student I’d be a bit peeved that the university sector were not at least showing willing in making that burden lighter.

Universities don’t give us knowledge – that’s down to us as individuals to hunt out, universities give us the tools to do that and the bit of paper that says we can do that.

Jun 26 2011

The Weekly Rage

Every week I listen to the Sunday programme on Radio 4, largely through inertia. Most weeks it manages to wind me up. I was a bit worried that I may be repeating myself here, so regular is the rage that I thought I must have written about it before. It turns out I have, but on a different topic.

The specific cause of my ire this week is the Church of England, the Equalities act and the inadmissibility of gay bishops. Forced by the Equality Act 2010 the Church has sought legal advice on how it should treat its gay clergy, it turns out they think that they may be obliged to accept gay bishops but that they can demand that they are celibate. You can read the BBC report here.

Why should this concern me, as a British atheist? Several reasons:

  • the Church of England is an established church, it takes (unelected) part in our legislation through the Lords Spiritual, it has a special position in teaching our children;
  • the Church of England claims moral authority, it specifically claims that it’s views on morality are superior to mine because they are faith-based. See the Bishop of Oxford’s comments this week on the Today programme;
  • I am ethnically Christian and English, so their position reflects badly on me;
  • the church’s position puts us all on shaky ground when we argue against inequality in other communities.

The Church could take a principled position that any group should be able to follow it’s faith: that the BNP should be allowed to exclude non-Caucasians from their number, for example. It could take the principled position that it should be subject to the same laws as the rest of us, without exemptions. It choses to do neither of these things, it choses instead to lobby for exemptions from the law and work out the minimum they can get away with in complying with that watered-down law.

What is the Church trying to tell us through this position? That the gays are OK, but not for them and not for positions of power?

Can you imagine a company, such as the one that I work for, demanding of it’s employee’s that they not only reveal their sexual orientation but also their sexual activity and if they confessed to the wrong sort of sexual activity they should be denied promotion?

Jun 25 2011

“Ridiculously long vacations”?

Lord Adonis, former education minister, is reported here as saying universities should:

…just abandoning these ridiculously long vacations … That only really makes sense as far as I can see if you want to travel the world or you need to get a job…

This is to misunderstand what happens during the long university vacation – the teaching staff, who are also research staff are getting on with doing research or, more painfully, trying to get funding for research. His point is not entirely without merit: universities have a distinctly schizophrenic attitude to teaching. If, as I have, you have applied for a number of lectureship positions you will learn that the time in interview dedicated to discussing your teaching experience, aspirations and ideas is approaching zero. Status in a university department depends largely on your research achievements, not your teaching achievements. This means there is scope in the market for universities that make teaching their priority, rather than research.

Jun 19 2011

Book Review: The Visual Display of Quantitative Information by Edward R. Tufte

 

tufte“The Visual Display of Quantitative Information” by Edward R. Tufte is a classic in the field of data graphics which I’ve been meaning to read for a while, largely because the useful presentation of data in graphic form is a core requirement for a scientist who works with experimental data. This is both for ones own edification, helping to explore data, and also to communicate with an audience.

There’s been something of a resurgence in quantitative data graphics recently with the Gapminder project led by Hans Gosling, and the work of David McCandless and Nathan Yau at FlowingData.

 

The book itself is quite short but beautifully produced. It starts with a little history on the “data graphic”, by “data graphic” Tufte specifically means a drawing that is intended to transmit data about quantitative information in contrast to a diagram which might be used to illustrate a method or facilitate a calculation. On this definition data graphics developed surprisingly late, during the 18th century. Tufte cites in particular work by William Playfair, who was an engineer and political economist who is credited with the invention of line chart, bar chart and pie chart which he used to illustrate economic data. There appears to have been a fitful appearance of what might have been a data graphic in the 10th century but to be honest it more has the air of a schematic diagram.

Also referenced are the data maps of Charles Joseph Minard, the example below shows the losses suffered by Napoleon’s army in it’s 1812 Russian campaign. The tan line shows the army’s advance on Moscow, it’s width proportional to the number of men remaining. The black line shows their retreat from Moscow. Along the bottom is a graph showing the temperature of the cold Russian winter at dates along their return.

800px-MinardInterestingly adding data to maps happened before the advent of the more conventional x-y plot, for example in Edmund Halley’s map of 1686 showing trade winds and monsoons.

Next up is “graphic integrity”: how graphics can be deceptive, this effect is measured using a Lie Factor: the size of the effect shown in graphic divided by the size of the effect in data. Particularly heroic diagrams achieve Lie Factors as large as 59.4. Tufte attributes much of this not to malice but to the division of labour in a news office where graphic designers rather than the owners and explainers of the data are responsible for the design of graphics and tend to go for the aesthetically pleasing designs rather than quantitatively accurate design.

 

Tufte then introduces his core rules, based around the idea of data-ink – that proportion of the ink on a page which is concerned directly with showing quantitative data:

  • Above all else show the data
  • Maximize the data-ink ratio
  • Erase non-data-ink
  • Erase redundant date-ink
  • Revise and edit.

A result of this is that some of the elements of graph which you might consider essential, such as the plot axes, are cast aside and replaced by alternatives. For example the dash-dot plot where instead of solid axes dashes are used which show a 1-D projection of the data:

ddp

Or the range-frame plot where the axes are truncated at the limits of the data, actually to be fully Tufte the axes labels would be made at the ends of the data range, not to some rounded figure:

range

Both of these are examples are from Adam Hupp’s etframe library for Python. Another route to making Tufte-approved data graphics is by using the Protovis library which was designed very specifically with Tufte’s ideas in mind.

Tufte describes non-data-ink as “chartjunk”, several things attract his ire – in particular the moiré effect achieved by patterns of closely spaced lines used for filling areas, neither is he fond of gridlines except of the lightest sort. He doesn’t hold with colour or patterning in graphics, preferring shades of grey throughout. His argument against colour is that there is no “natural” sequence of colours which link to quantitative values.

What’s striking is that the styles recommended by Tufte are difficult to achieve with standard Office software, and even for the more advanced graphing software I use the results he seeks are not the out-of-the-box defaults and take a fair bit of arcane fiddling to reach.  Not only this, some of his advice contradicts the instructions of learned journals on the production of graphics.

Two further introductions I liked were Chernoff faces which use the human ability to discriminate faces to load a graph with meaning, and sparklines – tiny inline graphics showing how a variable varies in time without any of the usual graphing accoutrements: – in this case one I borrowed from Joe Gregorio’s BitWorking.

In the end Tufte has given me some interesting ideas on how to present data, in practice I fear his style is a little too austere for my taste.There’s a quote attributed to Blaise Pascal:

I would have written a shorter letter, but I did not have the time.

I suspect the same is true of data graphics.

Footnote

Mrs SomeBeans has been referring to Tufte as Tufty, who UK readers of a certain age will remember well.