Making a choropleth map in QGIS 2.14 (Essen)

Time for my annual post! I’ve decided that instead of chatting generally about my Ph.D., I can use this site to record tutorials on the geographic and statistical techniques I am using. Hopefully someone finds this interesting, but it is also a useful public record of certain techniques for future reference for me or students. Today I worked out (quite simple, really!) how to make a simple choropleth map in QGIS 2.14 (Essen):

An example choropleth map I've made.

An example choropleth map of the density of Portable Antiquities Scheme finds from all time periods per parish.

 

Step 1: Start with two vector data types: one of points, the other of polygons. I have the metal-detector finds from all periods for Sussex (from the PAS database) and the digitised 1851 parishes from Kain and Oliver (200?). Note that some of the northings and eastings are incorrect!

Figure_1

Step 2: In the menu, choose Vector > Analysis tools > Points in Polygon

Figure_2

Step 3: Choose the layers you want to count. Your polygons are going to be the containers in which your points will be assigned. You can customise the name of the field which the sum of the points in the polygon will be recorded. You can also give your .shp file a name. When you’re ready, press ‘OK’.

Figure_3

Step 4: Voila! …Nothing happened. You get a new .shp file that looks exactly like your old one. If you open the attribute table, however, you’ll see the new field and numbers which represent the counts of points in each polygon.

Figure_4

Step 5: While we’re in here, we will replace all of the ‘NULL’ values in the field to ‘0’. We can do that with the ‘Select features by using an expression’ button. In this case we want to select all of the rows where the field “PNTCNT” is NULL. Press ‘Select’ and then ‘Close’. Go back to the attributes table.

Figure_5

Figure_6

Some rows should be selected. Make sure that the layer is editable (the pencil icon in the upper left corner) and that the field you want to edit is selected in the drop-down selection box. Put ‘0’ (without the inverted commas) in the box and click ‘Update Selected’.

Figure_7

Step 6: We can close out of the attribute table and go into the properties of the layer we created. Right click the layer in the ‘Layers’ panel and select ‘Properties’. In the style menu, we select ‘Graduated’ from the symbol selector at the top.

Figure_8

Step 7: I chose the blue colour ramp because it’s my favourite colour (inverted means the darker colour will be closer to 0, but as density of points it makes sense that the higher the quantity = the darker the colour. Feel free to pick any of the other colours or invert as you wish! Check out http://colorbrewer2.org/ which is a web tool for exploring the use of colour in map-making.

Figure_9
I also chose ‘pretty breaks’ for the classifications because round numbers, particularly in the hundreds, are psychologically satisfying.

The resultant map.

The resultant map.

 

The resultant map, inverted.

The resultant map, inverted.

In this case, the map is less than helpful, as there has been an awful lot of metal detecting in only a few parishes which drown out the results. In my case, the inverted option makes more visual sense. Experiment with other classifications to see which best represents your data. In this case a heat map would probably be a better option than choropleth, but it is best to consider what combinations of raster and vector data is more suited to the type of information you are trying to communicate.

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CityEngine and the potentials for visualising heritage

Visualising archaeological material is advancing at an alarming rate. The staggering profusion and increasingly affordability of 3D printers means that many people can own one or build their own, and potentially create their own museum. Like many people, I have a fringe interest in video games. Unlike many people, I am eager to become a developer (albeit at the hobbyist level) of interactive applications. 3D printing shows that the technology exists to accurately represent portable artefacts in 3D and accurate to 20 microns.

But what about something larger?

3D scanners have been employed to recreate the famous paleolithic caves at Lascaux to millimeter detail. The result is astonishing. But what about something even larger?

Anything bigger moves from the realms of laser scanning and 3D printing and into the realms of geographic information systems. Specifically, ESRI’s CityEngine software. While much of the tutorial content for the software relates to its use in modern applications such as the planning policy and the impact of construction in the urban environment, there are archaeological applications for large-scale representation. One such pioneering project is RomeLab. The description of the project in their own words:

RomeLab is a multi-disciplinary research group whose work uses the physical and virtual city of Rome as a point of departure to study the interrelationship between historical phenomena and the spaces and places of the ancient city. Using gaming technology, we created virtual worlds which are used in the classroom and in research experiments.

The increasing accessibility of powerful tools from both the geographic information side and the 3D games universe are converging to make this a really exciting time to work in archaeological landscapes. Software such as Unity3D, the Unreal Development Kit, and Cryengine are but a few of the potential engines to drive immersive archaeological landscapes forward. Perhaps with the assistance of consumer-grade virtual reality (VR) headsets such as the Oculus Rift, the HTC Re Vive and others will allow archaeological and heritage professionals to really assess the impact of the built environment both visually and in moving through the space. An example of the relevance to my own work is being able to visualise the Roman town of Noviomagus Regnensium (now Chichester) based on the 50+ years of reasonably well documented excavations conducted within the walled area of the town. By using this ‘certain’ data as a point of the departure, a model can then be built based upon qualifiable levels of certainty and thereby be able to withstand the scrutiny all academic work must endure.

Finally, there has been a huge push in making archaeological data open to the public. The potential impact of open spatial data such as OpenStreetMap and archaeologists making their data open to heritage organisations such as museums is huge. By embracing novel approaches archaeologist and museum professionals can demonstrate the relevance of their work by engaging the public imagination in a past that they are better able to feel. If we make individuals and communities feel more strongly that the past was a real place, there is a better chance that they will care about and for it.

Cissbury Ring – An early medieval ‘just-so story’?

Cissbury Ring

Photograph of the Iron Age ramparts of Cissbury Ring, near Worthing, West Sussex. The ramparts enclose a multitude of Neolithic flint mines and Bronze Age barrows can be found on the nearby downland. View is to the southeast. Photograph is a copyright English Heritage NMR.

The massive Iron Age hillfort at Cissbury was supposedly named for Cissa, one of the sons of the pseudo-mythological figure Ælle, who, accordingly to the Anglo-Saxon chronicle was purportedly the first king of Sussex and bretwalda of Germanic peoples south of the Humber. It has been argued that the town of Chichester (Roman Noviomagus Regnensium) was also named for Cissa and was the seat of his kingship after Ælle died, although there is apparently no evidence for sub- or post-Roman settlement within Chichester between the fifth and seventh centuries. Similarly, although there is evidence for occupation within the Cissbury earthworks from the neolithic until the end of the Roman period, excavations there have not found any evidence for early medieval settlement within the earthworks, nor indeed elsewhere on the surrounding downland.

It is clear from the Anglo-Saxon Chronicle that the Anglo-Saxons, even as late as the ninth century when those documents were compiled, were obsessed with genealogy, perhaps assuming that invoking potent ancestors, they promoted their own legitimacy. This has been argued as a reason for the placement of early medieval burials adjacent to, or within, earlier Bronze Age tumuli; in placing the bodies of their kin in association with earlier monuments, the social group attempted to exercise local territorial control. Local elites may have taken these famous `ancestors’ as real ones. A family of local importance may have fabricated descent from a figure known in stories which became the basis for the earliest entries in the Anglo-Saxon chronicle, just as King Alfred traced his family back both to the pagan god Woden and, ultimately, the biblical Adam. A kin-group would then advertise this legitimacy. In West Sussex there were the Wlencingas, descendants of another son of  Ælle, which became Lancing; or dwellers on the coast of Selsey where Ælle’s last son was purported to have landed became known as Cimenshore.

Distribution map of the place-names purportedly connected to the sons of Aelle, mentioned in the Anglo-Saxon Chronicle as the first Germanic king of Sussex. Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service

Distribution map of the place-names purportedly connected to the sons of Aelle, mentioned in the Anglo-Saxon Chronicle as the first Germanic king of Sussex. Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service

By imbuing the landscape with the names of mythical heroes and other dramatis personae, the people of Sussex may have reinforced a common social identity, possibly in the face of some type of stress. Sussex was conquered by Cædwalla of Wessex in 684 or 685 and no longer had its independence, becoming a satellite to Mercia in the eighth century and later a shire of Wessex during the reigns of Æthelwulf and Alfred. They were mentioned as a distinct group as late as the A.D. 1000s: a wave of Viking raids in the eleventh century was recorded as taking place “in the land of the South Saxons” in the first decade of that century. Perhaps in order to reinforce the sense of social identity, a myth sprang up about South Saxon glory of ages past. The people might have spoken of the legendary warrior Cissa who fought battles in the very lands where they walked, and erected impressive fortifications, such as those that still survive at Cissbury, but are in fact over 1,000 years older than the first Germanic settlers in West Sussex.

Place-names, archaeology, and boundaries of early medieval polities

The Mardens are so-called to refer, in the collective, to North Marden, East Marden, West Marden, and Upmarden, in West Sussex. The place-name is interpreted as containing the Old English an element from gemǣru, meaning `a boundary’ (Mawer & Stenton, 1969). This element is not unique to Sussex, nor to early medieval Britain as a whole; it appears in the Anglo-Saxon Chronicle in reference to a battle fought at mearcredesburna, the ‘boundary stream agreed to by treaty’ as well as referring to the Myrcna, the Mercians (the ‘Border People’), one of the largest and most powerful kingdoms in Britain until being subsumed by King Edward of Wessex after the death of his sister Æthelflæd in A.D. 918. Usage has survived into modern times to describe border areas or territories, such as the Welsh Marches, or an area inhabited by a specific people, such as Denmark.

Sketch map showing the location of the sites discussed in the text. The South Downs Way is the modern track as plotted on the modern Ordnance Survey map and may not reflect the precise route in antiquity. Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

Map showing the location of the sites discussed in the text. The South Downs Way is the modern track as plotted on the modern Ordnance Survey map and may not reflect the precise route in antiquity. Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

The importance of the ‘boundary’ interpretation of the Mardens lies in the exploration of the local topography and determining how the landscape was divided and between what political units. The boundaries of early medieval polities, whether they be estates or kingdoms, are typically vague and often rely on landmarks or extant features, such as Roman roads or burial mounds. ‘Marden’ can be either gemǣru-dūn, a ‘boundary-hill’, or gemǣru-denu, a ‘boundary-valley’. The topography is somewhat unhelpful in drawing out the meaning, as the undulating downland heights are broken by lower dry and intermittent/ephemeral stream valleys; the hill known as Apple Down is located above a dry valley which runs all the way from the coastal plain to the ridge of the northern scarp-slope.

A fifth- to seventh-century mixed-rite cemetery was discovered on Apple Down in 1981 and extensively excavated between 1982 and 1987 (Down , 1990, 9). Cemeteries as ‘places’ in the earliest medieval period served as foci where ideas of the past and present could be articulated such as claims over territory and resources and as statements of group identity (Williams, 2011, 255). It could be that the cemetery at Apple Down demarcated the western boundary of Sussex from its neighbour Wessex, where another topographic feature or settlement, served as a marker on the coastal plain. The South Downs Way is an ancient track which traces the scarp-slope on the top of the chalk downs and is marked along its extent with Bronze Age and early medieval tumuli and other monuments. The cemetery at Apple Down is only 4 km south of the South downs way; it may have been placed to reinforce a claim to land or resources and named to inform east-west travellers on that track that they were entering another territory.

Another possibility, if the ‘hill’ interpretation of Marden is accepted, is to consider that gemǣru-dūn refers to a much wider area than the modern parish that bears the name and demarcates a boundary between a polity on the coastal plain and one north of the downs in the Vale of the Western Rother, rather than eastern and western neighbours. A Roman road (Margary 155) from Chichester, perhaps to Silchester (Calleva Atrebatum), passes approximately 4.5 kilometres from Apple Down and was still in use in the earliest medieval centuries. In the passage over the downs, gemǣru-dūn may refer to the chalk downs themselves and represent a ‘boundary’ between discrete polities within a socially fragmented South Saxon kingdom, with power bases existing on the coastal plain, known to be at least the primary territory in the late seventh century of King Æthelwealh and a possible polity suggested here, in the Vale of the Western Rother, north of the scarp-slope of the chalk downs. The intersection of place-names and archaeology may represent folk-territories in southern England, and particularly Sussex. Place-names with patronymic elements occur in the possible folk-names Stæningas (Steyning) on the River Adur, the Piperinges (Peppering) on the River Arun (Semple, 2008). Such a model would accommodate a polity in the Vale of the Western Rother, between the South Downs and the Low Weald. This also perhaps sheds light on the riddle of why there are often concurrent kings of Sussex, of apparently parallel dynasties, witnessing charters when they begin to be issued after A.D. 700 (Kelly, 1998).

References:

Down, A., & Welch, M. (1990). Chichester Excavations 7. Chichester: Chichester District Council.

Kelly, S. E. (1998). Charters of Selsey. Oxford: Oxford University Press.

Semple, S. (2008). Polities and princes AD 400-800: new perspectives on the funerary landscape of the South Saxon kingdom. Oxford Journal of Archaeology, 27(4), pp. 407-429.

Williams, H., 2011. Mortuary Practices in Early Anglo-Saxon England. In H. Hamerow, D. Hinton, & S. Crawford, eds. The Oxford Handbook of Anglo-Saxon Archaeology. Oxford: Oxford University Press, pp. 238–265.

Sonnet on Selsey Cathedral – Anonymous

The sea now rolls in triumph o’er the ground
Where once thy sacred edifice was rear’d;
No mark, no stone, to trace thy wall is found;
All, all is gone, as if thou ne’er appeared.
But yet ’tis said, at midnight’s fearful tide,
When wintry storms in angry surges sweep
The shore, complaining spirits from the deep
Pour forth their melancholy voices wide,
Speaking an awful tale of former days,
How holy men were torn from saintly graves
Their bones neglected-scatter’d by the waves.
Rest, troubled spirits; and to Him give praise
Whom storms and tides obey; direct thy care
To Heaven not earth, for alls’ recorded there. (101)

Heron-Allen, E. 1911. Selsey Bill: Historic and Prehistoric. London: Duckworth.

Abstract Submitted for EMASS 2013

Here is the text of the abstract of the paper I intend to give at the Early Medieval Archaeology Student Symposium, 20-22 May 2013 hosted by the University of Chester:

This paper presents the findings from a recent geophysical and topographical survey carried out in Church Norton, West Sussex. Church Norton is the name given to a hamlet in the north-east corner of Selsey parish at the mouth of Pagham Harbour, south of Chichester. This region is widely known for its rich Roman archaeology; however, an extensive 30-acre magnetometry and topographic survey will explore remnants of early medieval occupation at Church Norton. More specifically, these surveys aim to determine the evidence for an early medieval monastic complex. Writing via West Saxon sources which recounted the life of Wilfrid of Northumbria, Bede reports that the South Saxon kingdom “remained persistently heathen until this time [AD 684], on account of its thick forests and rocky coasts”. However, Wilfrid was received by King Æthelwalh and given a villa regalis and 87 hides to establish a monastery on the island of Selsey which eventually came the first seat of the South Saxon Bishops. The fate of Wilfrid’s monastery has been variously argued in the literature: a natural hillock called “the Mound” at Church Norton and the remains of a twelfth century church could represent the site of Wilfrid’s monastery; antiquarians on the other hand, believed that erosion had claimed the site. The results of these surveys will add a new dimension to this debate and direct future work.

As this is my first real academic conference, I am over the moon to be considered to present although my work is still in its early days.

Case-Study Location: Westhampnett

The civil parish of Westhampnett, 2.5km northeast of Chichester, encompasses two modern settlements: the village of Westhampnett on the south boundary of the parish adjacent to the A27 and the hamlet of Westerton a kilometre to the northeast. A low, but ‘locally prominent’ hill on the border of Westhampnett and Oving parishes was the focus of ritual and burial activity from the pre-Roman Iron Age to the seventh century.

The early medieval cemetery was initially identified during archaeological mitigation work during the construction of the A27 Westhampnett bypass in 1992 (Fitzpatrick et al., 1997)⁠. Two Roman roads, from Chichester and heading northeast to London and east (presumably) to Brighton, cross through the parish. Pieces of Roman brick, box flue and hypocaust tile are built into the walls of the parish church (Hills, 1869, 41 & Fig. 3)⁠. These pieces may have been robbed from Chichester, or a yet unknown villa in the vicinity (Hills, 1869, 37-43; Russell, 2006, 291)⁠.

Excavations in advance of the A27 Westhampnett Bypass uncovered an early Anglo-Saxon cemetery and pushed the earliest Germanic acculturation of the westernmost coastal plain back to the sixth century (Fitzpatrick et al., 1997)⁠. Discovery of early medieval occupational evidence during rescue excavations in the year 2000 and 2001 is suggestive of a settlement contemporary to the cemetery (Chadwick, 2006)⁠. Two “apparently isolated” sunken-featured buildings were discovered, but it “cannot be excluded that some of the undated post-holes within the area of the Bronze Age settlement.. are Anglo-Saxon in date” (ibid. 24). A total of 176 sherds of pottery, identified as Early/Middle Saxon on account of their similarity to assemblages from the Apple Down cemetery and places it within the Sixth to Seventh Centuries. Early and Middle Saxon pottery is “notable on account of its scarcity” and the possibility of linking a contemporary settlement with another rarity, an early medieval cemetery on the coastal plain, could potentially be demonstrative of ‘everyday’ expressions of identity within a domestic context.

Chadwick, A. (2006). Bronze Age burials and settlement and an Anglo-Saxon settlement at Claypit Lane, Westhampnett, West Sussex. Sussex Archaeological Collections, 144, 7–50.

Fitzpatrick, A. P., Powell, A., James, S. E., McKinley, J., Mepham, L. N., & Montague, R. (1997). Archaeological Excavations on the Route of the A27 Westhampnett Bypass, West Sussex, 1992. (J. Gardiner, Ed.). Salisbury: Wessex Archaeology.

Hills, G. (1869). The Church of West-Hampnett. Sussex Archaeological Collections, 21, 33–43.

Russell, M. (2006). Roman Sussex. Stroud: Tempus.