| Surveying
Saxton's Hampshire 1575
|
|
questions
|
If we want to know how Christopher Saxton did his mapping we
should ask:-
- what documentary evidence is there, directly pertinent to
Saxton's project?
- what technical knowledge was available to him; surveying
techniques, textbooks, instruments?
- what existing data was available?
- how much time did he have?
- what can be deduced from his maps?
And: we should not make wild guesses founded on the wishful
thinking that we will be able to answer the question.
|
evidence
|
DOCUMENTARY EVIDENCE
Christopher Saxton left us no notes about his surveying methods;
and wrote no handy textbook on surveying (as did John Norden who
began a county survey in the 1590s). And there are few surviving
relevant documents:-
Local Knowledge
To aid him in his task in Wales Christopher Saxton had an open
letter from the Privy Council, addressed to Justices of the Peace
etc, 10 July 1576:-
An open Lettre to all Justices of peace mayours & others etc
within the several Shieres of Wales. That where the bearer
hereof Christofer Saxton is appointed by her Maiestie under
her sign and signet to set forth and describe [Cartes] in
particulerlie all the shieres of Wales. That the said
Justices shall be aiding and assisting unto him to see him
conducted unto any towre Castle highe place or hill to view
that countrey, and that he may be accompanied with ij or iij
honest men such as do best know the countrey for the better
accomplishment of that service, and that at his departure
from any towne or place that he hath taken the view of the
said towne do set forth a horseman that can speke both
welshe and englishe to safe conduct him to the next market
Towne, etc.
A similar letter of instruction was issued by the privy Council for England, 11 March 1576:-
A placart to ... Saxton servant to Mr. Sackeforde, Mr. of
Requests to be assisted in all places where he will come for
the view of mete places to describe certen counties in
Cartes being thereunto appointed by her Majestes bill under
her signet
Beacons and Churches
Beacon hills are some of the obvious high places. The beacon
system in England dates back to medieval times, perhaps earlier.
The organisation of the beacons devolved to Justices of the
Peace and other officers at the local level. They would know
them, they had honest men who knew the view and could identify
places from them for a surveyor. It is very likely such places
might be used by Saxton. But, judging from one county,
Hampshire, a doubt creeps in. He did not plot all the beacons
in the county; so did he use all of them, or even any of them?
Bear in mind that it may not be the hill's top that is the best
viewpoint. If you look at known beacon locations they, too, are
not always on the tops of hills or even the very highest local
hill. What you can see from the position matters more than just
height. Church towers are other obvious view points though
nowhere as good as high hills; churches were the common starting
point for estate surveys at the time.
If all this sounds fairly straightforward I suggest you go out
to a local viewpoint and see how easy it is, or isn't, to spot
useful places, church towers of the villages you might wish to
plot for example. Discover how many of them are not visible from
the place you have chosen. Also just see how well you can
recognise places from afar.
|
methods & tools
|
SURVEYING TECHNIQUES and INSTRUMENTS
There were two main ways of surveying; triangulation and
traverse; crude traverse and accurate triangulation are two ends
of a spectrum of surveying techniques. Traverse was the
practical surveyor's method of earlier times. Triangulation
required some understanding of geometry. There was a difference
between what mathematicians knew and could do, and what the
practical surveyor did. The period was one where there was
increasing interest in navigation, using astronomical observation
more systematically; military science was using geometry for
gunnery; and agricultural changes required more accurate
definition of boundaries.
Traverse
Traverse is the way of direct measurement; compass, measuring
ropes, poles, or chains, or a waywiser. You measure bearings and
distances from point to point to point and plot your route, like
dead reckoning navigation. If the traverse is closed, you end
up where you started, and then you have a way of checking your
accuracy; see if the plot also arrives back where you started.
Then if there is an error you can make adjustments all along the
plot to improve things. If the traverse is open you need some
other way of knowing whether the two end points are correctly
positioned with respect to each other. You might measure offsets
to features beside the path of the traverse, take a bearing to
the feature and estimate or measure its distance. This might be
aided by a surveyor's cross staff, the Roman's groma, to set a
right line to an offset target.
The obvious routes for traverses were roads. Christopher Saxton
did not plot roads on his maps. The social, economic and
military importance of roads was recognised at the time. If
Saxton had done everything by road traverses it is hard to
believe that he would not have plotted these roads. He did plot
rivers; perhaps he made traverses up river valleys.
Compass Sketches
Edward Lynam's view, writing in 1936, is that, like most estate
surveyors, Christopher Saxton would have started his survey from
church towers establishing angles to other towers and hills by
compass and cross staff. He would have got distances from local
knowledge or perhaps by riding from place to place; he would not
have used the slow laborious method of 'chaining' distances. It
is possible he used a waywiser. His maps are 'compass sketches',
a traverse, yes, but in a very rough and ready way. It is the
method of 'view and inquisition' the traditional manner of
surveying estates from the Middle Ages to the 19th century.
A Professor Manley's opinion was that Christopher Saxton:-
... climbed very few hills; as a rule only when it appeared
to him that he could thereby save a further traverse into
sparsely inhabited country ... He was conscientious with
regard to county boundaries and other detail in the
cultivated lowlands, but wherever possible he avoided the
trouble of going beyond the limits of habitation through
country which he knew or thought to be uninhabited,
especially if he was thereby led into another county.
This opinion came from a study of the finished maps of some
northern counties. It is a reasonable supposition, but that is
all.
Triangulation
Triangulation was first described fully by Gemma Frisius or
Phrysius. He was a leading cartographer in Europe, alongside
Gerhard Mercator. Frisius published an edition of the
Cosmographia by Petrus Apianus, Peter Apian, 1529. In an edition
in 1533 he bound in work of his own, known as the Libellus [1,
see appendix]. Triangulation uses the fact that knowing the
distance between two points and the bearings of a third point
from the ends of this base line, you know where the third point
is. Angles must be measured more accurately.
In the Libellus Gemma Frisius describes what he claims to be a
new method, his invention, of surveying without direct
measurement, using an instrument derived from the pivoted sights
and angular scale on the back of the astrolabe, an astronomical
instrument in common use at the time. Holding an astrolabe
sideways, so that its back scale is horizontal you can measure
bearings. Frisius makes this an instrument in its own right.
- [2] - The instrument is a graduated circle on a flat board,
fitted with a central pivoted pointer with sights, as would be
found on the back of an astrolabe.
- [3] - Set the instrument level with a nautical compass on top to line it up on magnetic north. That magnetic north was used is made plain in Apian's part of the book, where there is a woodcut print, in editions from 1524 onwards, showing the compass needle 8 degrees East of North, the magnetic variation in the early 16th century. Once set up the compass is not required for the surveying instrument. The bearing to any point can now be found, keeping the instrument fixed.
- [4] - A critic is imagined saying what's the use of bearing
without distance? Indeed there must be bearings from two places
before the position of a target place is fixed. So the surveyor
must repeat the operation from a new vantage point.
Then:-
(translated by E G R Taylor?) When you have found them [the
second set of bearings] make a dot for this [second] town
at any distance you please from the first, provided it is
on the right ray [correct bearing], and with this point as
centre draw a faint circle, and through it a meridian
parallel the first [through the first town]. Next draw from
this point lines representing the bearings just found, and
wherever a pair of rays drawn to the same place intersect,
a little dot must be placed, which represents its position.
Gemma Frisius deals with some detail problems, for example what
to do when rays meet at too oblique or acute an angle. He points
out that distances found by a traverse, measuring on the ground,
are inaccurate; not helped by irregular spacing of milestones.
But you do need to know at least one distance between stations
to set a scale for the map.
Frisius calls the new instrument a planimetrum, and later uses
a greek word epipedometron. It is usually known now as the
'simple theodolite'.
As well as authors noted below there was a textbook on surveying
by Valentine Leigh, Treatise of Measuring All Kinds of Lands,
1562 (only extant today in editions from 1577 onwards).
Simple Theodolite
William Cunningham, in his Cosmographical Glasse, 1559, explained
triangulation, acknowledging Gemma Frisius, and described the
instrument needed as a 'geographical plaine sphere' - a
planisphere is an element of an astrolabe. A circular plate
'made much like the backe parte of an Astrolabe' with a pivoted
alidade, the sights. His scales were marked with the 32 points
of the compass, and also from 0..90 degrees in each of four
quadrants. The instrument had an inset magnetic compass for
alignment.
In 1571 William Bourne prepared for publication a manuscript of
popular science in which the second part deals with surveying;
by the 'back side of the astrolabe', by cross staff, and by
triangulation much as described by Gemma Frisius. This
manuscript was presented to Lord Burghley who was sufficiently
interested to talk to the author. William Bourne describes a
practical surveying compass, closely based on the description by
William Cunningham, neither of them making claim to originality.
Bourne's description is of an instrument with a circular brass
plate, graduated round the edges in degrees and marked with the
32 points of the compass. A magnetic compass is inset off centre
so that does not get in the way of the pivoted 'athelidey' ie
alidade, which is like that on the back of an astrolabe.
This 'simple theodolite' is commonly just called a theodolite
in elizabethan and later texts, which confuses it, for us, with
the modern theodolite. The modern surveyor's instrument is not
just an azimuth but an altazimuth instrument measuring up and
down as well as from side to side, sighting through a telescope.
In its turn, this instrument is being replaced by laser devices
making digital records.
Thomas Digges in his Geometrical Practise named Pantometria,
1571, uses the term theodolitus ie theodolite for the simple
theodolite. It was a popular instrument, a successful invention;
do remember that not all inventions were or are effective. The
theodolite is mentioned by John Norden in his Surveyor's
Dialogue, 1607. John Norden was another elizabethan surveyor,
who mapped several counties in the 1590s but failed in his
overall project of a new county mapping.
Plain Table
It seems that practical but complacent surveyors, long used to
their ways of working, were resistant to newfangled mathematical
ideas arising from a resurgence of the art of geometry. The view
is widely held today that the average surveyor of elizabethan
times could not cope with the simple mathematics required by the
geometrical instruments. Out of the surveyor's practical needs
comes the invention of the plain table and sight rule,
triangulation without arithmetic.
The first step was an instrument called a holometer, devised by
Abel Foullon in his book Holometre, Paris, 1551. This book was
widely circulated, and was translated into Latin and Italian from
its original French. The holometer is a complete field
triangulation and plotting instrument; a table for the paper with
an inset compass, a brass graduated base line scale on which two
arms slide so they can be set a required distance apart for two
observation stations, each arm pivots and has sights, etc. It
was a cumbersome tool, a reminder of later victorian universal
tools which were more bother than help. But the instrument
introduced the idea of plotting in the field. And then an
unencumbered, plain, table with a sight rule, an alidade and
ruler to set on top, was a much more practical step.
The idea is simple. You have a flat table mounted on a tripod
stand, in the field, and on this a sheet of paper. There are two
fixed stations; which are marked a distance apart on the paper,
setting the scale of the map. At station 1 you set up the plain
table with the line joining the stations pointing at station 2.
With a sight rule, you draw lines out from the plotted position
of station 1, each labelled for their target. At station 2 you
line up the table again looking back to station 1, then take
sights and draw lines to each of the targets. Where
corresponding lines cross you plot the target place.
Ralph Agar, writing A Preparative to the Platting of Lands,
London, 1596, says that early in his career as a surveyor, about
1566, he used the 'plain' table:-
sometimes directed by needles [ie set up by magnetic
compass], sometimes by the former station [ie by a back
sight onto station 1 from station 2] as is now used
By 1571 he abandoned the plain table for the 'theodelite'.
Thomas Digges adds the plain table to his textbook on surveying
in the 1591 edition, describing it as:-
a Platting Instrument for such as are ignorant of
Arithmetical Calculations ... an Instrument onely for the
ignorant and unlearned, that have no knowledge of
Noumbers'
... you must in this kind of Platting proceed wonderfull
warelye, for if you erre never so little in the severall
Stations, when yee come to close uppe the Platte, you shall
finde a great and apparent Error ... [to be adjusted] ...
by cross Angles of Position.
The plane table is offered as an immediate and practical
alternative to recording bearings in a notebook and doing
the plotting back at base, where you 'lay down' or 'protract'
measurements. Plotting at base has no need for arithmetic, so
resistance to working this way is hard to understand. It is done
in easier circumstances than standing on a windy wet hilltop
trying to keep paper clean and dry ... As Thomas Digges said,
plain tabling is:-
... not to bee practized but in fayre weather ...
We have read at least one 'fact' in a supposedly respectable book
about cartography that Saxton made pages of notes of bearings as
he travelled about the counties, presumably read from a simple
theodolite. In the book this is unsupported by any reference to
sources, and we know of no such source.
Arithmetic?
There are contemporary comments about the habits of surveyors:-
- that they multiplied length by width to get area without any
regard to the angle between the two dimensions;
- estimated angles by eye, not using an instrument;
- estimated area by averaging the four sides of a plot, and
squaring the result;
- estimated the area of a circle by dividing circumference by four and squaring the result.
The opening pages of books like Digges's go to some length to
deal with the principles of geometry!
|
data
|
KNOWN DATA
Christopher Saxton could have had access to some general maps of
England and Wales. Laurence Nowell had published a small map,
1563:-
A general description of England & Irela~d with ye costes
adioyning
and Gerhard Mercator, 1564:-
Angliae Scotiae et Hiberniae nova descriptio
These are too small a scale to be of great use, though matching
the content of these with the county maps might reveal some
relationship. A set of maps that is now gone could have been
consulted; maps by Laurence Nowell used by William Lambarde, a
kentish antiquary writing a topography of England about 1568-77.
These sources are discussed more fully by Huddy and Tyacke 1980,
who also discuss the making of the general map of England and
Wales more fully.
|
time
|
TIME
Christopher Saxton surveyed all the counties in five seasons of
surveying. Not as much as a month per county. Nowhere is there
any mention of assistants to help. His project was an official
survey, promoted by Elizabeth I on the advice of her ministers
as an act of policy. It had to be completed quickly to be
useful.
The time scale precludes any sort of rigorous, close surveying.
Topographical detail must have been culled from where he could.
There were sources of information, general maps like: the map
of the British Isle by Gerhard Mercator, 1564; the map of England
and Wales by Humphrey Lloyd, published by Ortelius, 1573. And
descriptive material like: John Leland's Itinerary of his
journeys in England; perhaps data from William Lambarde, who was
then writing a Topographicall Dictionarie of England.
|
maps
|
THE MAPPING
We have investigated one county map, of Hampshire, in more
detail. Measuring the position of a number of places on the map
and comparing these to their 'known' positions. From these
measurements it is possible to work out the true scale of
Christopher Saxton's map and express this in statute miles to an
inch, and thus work out the size of Saxton's mile as drawn in his
scale line. His 'old english mile' is about 1.23 statute miles.
The orientation of the map can be checked, it is plotted about
7 degrees east of national grid north, roughly matching the
magnetic variation of elizabethan times. A correlation of his
place positions to today's positions gives a crude measure of how
good his map was. An attempt to determine his surveying methods
would require detailed study of the positioning of settlements,
rivers, hills, coast line. We believe this would be
inconclusive.
Another possible line of enquiry is to compare Christopher
Saxton's separate county maps with his general map of England and
Wales.
|
answer
|
ANSWERS?
How did Christopher Saxton survey? we cannot know.
It is quite likely that Christopher Saxton could have had access
to good instruments, he was working for a government project and
Lord Burghley had an interest and knowledge of techniques of the
time. It is possible that Saxton had a waywiser and compass,
etc; simple traverse instruments. It is possible that Saxton
could have had a simple theodolite and worked by triangulation,
plotting data in the field or back at base. Such an instrument
could have come from the leading instrument maker of the time,
Humphrey Cole, who was known to Lord Burghley who was behind the
mapping project.
But the time scale suggests that Christopher Saxton worked from
crude traverses supported by local knowledge; he could not have
got the job done so quickly otherwise.
(These notes were written in response to an enquiry
from a BBC researcher, planning a program about
elizabethan technology
|
books
|
REFERENCES
Bennett, J A: 1987: Divided Circle: Phaidon & Christies:: ISBN
0 7148 8038 8
Harley, J B: 1977: Christopher Saxton and the First Atlas of
England and Wales: Map Collector: vol.8: pp.2-11
Lynam, Edward: 1936: (Introduction to a facsimile reproduction
of Christopher Saxton's Atlas of England and Wales): British
Museum (London):: NLS Map.Fac.b C17 (1579)
Manley, G: 1934: Saxton's Survey of Northern England:
Geographical Journal: vol.83: pp.308-316
Norgate, Martin & Norgate, Jean M: 1996=2002: Old Hampshire
Mapped::: website www.geog.port.ac.uk/webmap/hantsmap/
Ravenhill, William (introduction): 1992: Christopher Saxton's
16th Century Maps: Chatsworth Library:: ISBN 1 85310354 3
Taylor, E G R: 1968: Tudor Geography 1485-1583: Octagon Books
(New York, United States)
Tyacke, Sarah & Huddy, John: 1980: Christopher Saxton and Tudor
Map Making: British Library:: ISBN 0 904654 44 3
|
latin
|
APPENDIX - Latin Text etc
Apian, Peter & Frisius, Gemma (ed): 1533: Cosmographia:::
folios 58-59:-
- [1] Item ejusdem Gemmae Phrysii Libellus de Locorum
describendorum ratione, et de eorem distantiis inveniendo,
nunquam ante hac visus.
- [2] Primum in assere plano confice instrumentum tale, fiat
circulus, qui in quatuor quadranto dissecetur, quadrante
quolibet rursus diviso (ut solet) in 90 gradus, postea
affigatur per centrum index cum perspicillis aut pinnulis
quemadmodum in dorso astrolabii
- [3] Hoc instrumento facto opus erit etiam instrumento nautico
(quod Compassum appelamus) nam ab illo fere tota res pendet,
quibus habitis ita procedito. Pone instrumentum planimetrum
primum in plano, et super ipsum Compassum, ita ut latus
Compassi quadrangularis adjacet linae meridinae instrumenti
inferioris. Deinde verte instrumentum cum compasso eo usque
quo index compassi correspondeat sibi subscripto indici, et
post haec instrumento ita manente, compassum tanquam
perfunctum suo officio remove.
- [4] Si nunc angulum positionis alterius loci a tuo scire velis,
manente instrumento immoto, volve indicem donec per
persicilla ejas videas locum alium, videbis mox angulum
positionis a meridie vel Septentrione secundum ipsius
indicis remotionem ab eis. Sed quorsum haec? roget aliquis,
etiam si habeam ab uno loco positiones vel situs omnium
locorum, si non adsit distantia nota, nihil profuerit. Verum
dicis ab uno loco, nam nisi a duobus locis habeas angulos
positionum, non poteris describere tertium.
|