Time geography, GIS and archaeologyDimitrij Mlekuž and Frank Vermeulen

UGent

Time geography

Torsten Hägerstrand

Space, time and human conditions. In: Dynamic

allocation of urban space, A. Karlqvist et al. (Eds.), 1975.

Pred A., (Ed.) Space and time in geography: Essays

dedicated to Torsten Hägestrand., 1981.

periods spent traveling (in black) and at work (cross-hatched). This use of a pseudo-threedimensional representation suggests an obvious potential for computer graphics.

Figure 3: Example of an individual’s path in a time-space coordinate system

(Source: Carlstein et al., 1978, p.164)

These examples concern the movement of a single individual, but how can we best presentthe experience of a group? If we are limited to graphics that can be reproduced on paper, webegin to run short of dimensions: if one dimension is time and another is used to distinguishindividuals, how can we show where they moved? These constraints lead naturally to our firstlifeline diagram, where each career is shown by a single line or bar and event are indicated bysymbols or changes in fill patterns along the bar. For example, the following diagramsummarises the migratory history of a large group of members of the Steam Engine Makers’Society. The Figure 4 is a simple bit-map graphic, but it forms part of a far more complexexample exploring the idea of ‘drill-down’.

To provide some background to this diagram, the late 1830s and early 1840s, the middleof the time-lines, were a period of severe recession (associated with Chartist unrest) and itwould seem to have affected the north-west of England and towns such as Bolton particularlyseverely. As a result, many engineers were forced to look elsewhere. The members of thistrade union were able to obtain financial assistance from other branches as they traveledaround, and from this we have very precise records of their movement. Note that about half

from Carlstein et. al 1978, 164

“The Choreography of Existence”

space

time

path bundle

“Aquarium”, Path, Bundle, Prism

space

time

potential path area

prism

from National Geographic 2007

Reconstructed spacetime path of the last hours of Ötzi

Temporality of Daily Routines

from Whytle 1954, quoted in Fahlander 2003

space

time

potential path area

prism

Spacetime prism

A

A

PPA

t0

t0+d

t0+2d

Tim

e

Space

from Gaffney and Stančič 1991

f(A)

p(B)

PPA(t)=f(A,t)∩p(B,t)t

PPA

BA

Space

Tim

e

Prism(friction, start, end, time)

Friction

AB

Start and end points

Time120 min

Timespace prism

Path/Prism intersection

Prism/Prisminterection

A

BC

tCS

tCE

A

B

C

D

Same prisms, different offsets, different intersectionsT

ime

Space

d0 d1 d2

PPA from Ricina to Trea

PPA from Ricina to M. Franco

PPA Intersection

Cumulative PPA, 30 min

Cumulative PPA, 60 min

“Landscape Accessibility”, Potential path field, t=30 min

“Landscape Accessibility”, Potential path field, t=60 min

Extending GIS-based visual analysis 37

Figure 8. Profile of linear features (e.g. a path) on a total viewshed.

and a pronounced increase in visual magnitude. The path then drops sharply into asecond possible enclosure, not as deep as the first one, with pronounced boundaries.After an extremely steep ascent the visual magnitude plunges down dramaticallytowards the end of the path.

3.3. V isual prominenceAn (intuitive) understanding of something being prominent in space arises after

some sort of comparison has been established between the level, or amount, of someproperty (p) at a location (l ), with those found at adjacent locations. Thus it can besaid that some idea of neighbourhood, i.e. what constitutes neighbourhood, is impliedin the comparison. Many criteria may be used to define what is a neighbourhoodor what locations are part of it, here a neighbourhood will be defined by referenceto an arbitrary Euclidean distance around any location. The area, comprising alllocations within this radius, will define the neighbourhood at any location. Once aneighbourhood is defined, it is possible to produce a simple definition of prominence,

Prominence of a property p, at any location i, Prom(t )pis defined as the average di!erence

between the property at that location p(i ), and that found at each of the other locationsjn, p( jn), within an arbitrary neighbourhood of i, N

i, such that given an arbitrary distance

where Niis the neighbourhood of i, N=Card(N

i) and nµN (Natural numbers).

i Prom(i )p=!jnµNi

p(i )"p( jn)

N(2)

The values for the prominence at any location can have any positive or negativevalue. The upper and lower bounds will change with each neighbourhood size. Thevalue and sign of the prominence reflects the morphological character of the location.For example, when calculated using a DEM, i.e. altitude being the property that isbeing compared, higher positive values tend to indicate a sharper hill-top, whilemore moderate values point towards a more rounded hill-top; values close to zeroindicate flat locations and negative values channel- or pit-like locations. It is import-ant to note that the definition at this stage does not include any sort of normalization.This is because the index may be normalized in various ways; the normalization ofthe entire raster by the maximum prominence value produces a result that is informat-ive, if the analysis is restricted to one image and to its entirety. However, if the

Prominence filter

Llobera 2003, 37

Accessibility prominence, t=30 min, r=75 m

Accessibility prominence, t=30 min, r=150 m

Accessibility prominence, t=30 min, r=300 m

...it forces us to think about time.

...it tells us about possibilities only, and nothing more.

Why time geography?

...it stresses the significance of material world and its constraints.

Acknowledgements

Potenza Valley Survey http://www.flwi.ugent.be/potenza/

Project Radio-Past http://www2.radiopast.eu/

{dimitrij.mlekuz, frank.vermeulen}@UGent.be