Mapping the Mapping Project’s Design

On Wednesday of last week I had a fantastically productive meeting with my colleague and GIS architect for the PBMP, Alexander Stepanov. In about an hour we defined the current state of our mapping project, reconceived and reified how the GIS would move forward, and established how it will function as the “pivot” for the other elements of the PBMP. Below is an image of the white board we marked up over that hour:


Much of this was already in our heads or sketched in broader terms in the notes of other meetings. What was different in this meeting was the previous four months of work to understand the production of the spatial data and to describe it in a specific and unique nomenclature. With this new foundation and confidence it was easier to define the phases of development and know how to realize them. From the image you might see these development phases of the GIS scribbled in my impenetrable handwriting. Here they are with a bit more detail:

Phase One: A Basic Map for Navigation. The first step in our plan (and the primary functionality intended for our GIS) is a map that allows one to effortlessly move across the landscape of Pompeii, to shift scales, to add and remove data layers, and to access the basic descriptive data of those layers. As I mentioned previously, we have focused on a subset of our spatial data for the Navigation Map. These layers are largely topographic rather than interpretive in their content:

GIS Name (Prefix_short-Name_Extent_Type_Version) Alias Code
PMBP_Alley_City_Poly_001 Alleys ALS
PMBP_FtWall_City_Poly_001 Fortification Walls FTW
PMBP_Curb_City_Poly_001 Curbstones CBS
PMBP_Elev_City_Pnts_001 Elevation Points ELP
PMBP_Forum_City_Poly_001 Forum FRM
PMBP_Fount_City_Poly_001 Fountains FNT
PMBP_Gates_City_Poly_001 Gates CGT
PMBP_Ins_City_Poly_001 Intersections INT
PMBP_PropWalls_City_Line_001 Property Walls (Muri) PRW
PMBP_NSS_City_Poly_001 Narrowing Stones NSS
PMBP_ProjIns_City_Poly_001 Projected City Blocks (insulae) PJI
PMBP_ProjInt_City_Poly_001 Projected Intersections PJT
PMBP_ProjStr_City_Poly_001 Projected Streets PJS
PMBP_PropEsch_City_Poly_001 Properties by Eschebach PRE
PMBP_RutsTsuji_City_Poly_001 Ruts by Tsujimura RTS
PMBP_Sidwlk_City_Poly_001 Sidewalks SDW
PMBP_SSS_City_Poly_001 Stepping-Stones SSS
PMBP_Str_City_Poly_001 Streets STR
PMBP_UnEx_City_Poly_001 Unexcavated Areas UNA
PMBP_WatTow_City_Poly_001 Water Towers WTS

Embedded in the nomenclature are elements of the data structure itself, including the data’s producer, an abbreviated indication of the content, its scale, the geometry type, and a version number. Thus,  the file name “PBMP_Forum_City_Poly_001” expresses that the file was made by the PBMP, encompasses the area of the forum, operates on the scale of the city, is a polygon, and is version 1. A more human readable alias is also included, as is a unique three letter code that serves as a prefix in the IDs of individual objects within that layer. In this case, there is only one Forum at Pompeii, so the polygon named FRM000001 describing it is the only feature in that layer.

To finish the Navigation Map we have only a few simple tasks to complete, including finalizing the metadata description of each layer, defining which parts of that metadata should be displayed when the user accesses if via the map (“identify tool”), and globally adjusting the position of our files to overlie publicly available satellite imagery. This final task is a kind of compromise between absolute accuracy and usability. That is, because a perfectly precise positioning of our Pompeii data would likely move it closer to the satellite imagery but not exactly overlie it, it is preferable to produce our data in a way that better meets user expectations and better integrates with other applications. If we have to be “wrong”, let’s be wrong in the right direction.

Phase Two: An Information / Interpretation Map. The landscape of Pompeii will become far richer as we begin to add illustrative and academic information about each of the objects in the map. We already link each property to Pompeii in Pictures, but the addition of information on each property from the Corpus Topographicum Pompeianum (CTP) will offer a full listing of all the names given to these properties as well as a basic bibliography for each. Such bibliographic content, together with the spatial index provided by Garcia y Garcia in the Nova Bibliotheca Pompeiana, will provide the first connection to our catalog of citations (see below for more on this).  In Phase Two we will also include functional interpretations. City-wide interpretive data come from the CTP and, of course, from the Eschebach plan of Pompeii. The 1993 update of this plan in Lislotte Eschebach’s Gebäudeverzeichnis und Stadtplan der antiken Stadt Pompeji also contains additional information about each property, such as dates of excavation, finds, and decoration as well as additional bibliography. We are in process of adapting this information as well. To provide more up to date functional information, we will also be including the published work of scholars who have focused on specific properties or types of properties, such as bars (Ellis), fullonicae (Flohr), or bakeries (Monteix). Finally, to increase the spatial resolution of the map, we are creating room level data based on the definitions and nomenclature in the Pompei: Pitture e Mosaici volumes. Producing spatial data at this level will offer the potential to attach research data in a more specific and powerful way, such as the finds-by-room data produced by Penelope Allison.

To do all of this work will require an investment of time to ensure the spatial and descriptive integrity of every  building the ancient city. On the descriptive side, this work will start by getting the building’s address correct and associating that with all previous addresses. Luckily, the CTP has published concordances from which to work. For the spatial side, there is no such index. Each building in our map will need to be examined and compared with previous maps to ensure that when we attach functional or interpretive data to a property, that property is the expected shape. For minor differences, especially in the interior of a single building, those differences will be described in the metadata and illustrated in georeferenced plans (when possible). For major differences, a new polygon will be drawn to reflect the different interpretations of a building’s shape. While a faithful representation of multiple interpretations is appropriate, it will also necessitate further attention to how different elements of the map interact with one another. This is called topology.

Phase Three: A Query Map.

Topological rules are the basis for one of the most powerful aspects of geographical information systems: the ability to search spatially. A spatial search can be on strictly spatially descriptive attributes, such as the elevation of a point, the length of a line, or the area of a polygon. It can also be used to find non-spatial attributes attached to the same geometries: the source of the point’s elevation data, the name of the street the line defines, or kinds of floor treatments of a room’s polygon. Most importantly, the spatial relationships among geometries can also be searched. That is, one could ask if a kind of room were found within houses of a particular size or if that house was within a certain distance of another kind of property, such as an inn or bakery. To generate this valuable kind of search depends upon three components:

  1. How well defined the physical shape of Pompeii is;
  2. How much academic information we can attach to those shapes;
  3. How carefully and precisely we define the topological rules.

Part one is well underway as our Navigation Map. Part two is growing, but always needs more information. Help from the community is ALWAYS desired. Part three, the Queryable Map, is in the very near future.

Phase Four: Pompeii’s Bibliocartography.

For the PBMP, the essential and defining query – whatever its structure – is to access accurate bibliographic information through the map. Realizing this functionality is fortunately not a terribly complex technological problem. Because of its robust native query functions, GIS  will be the primary platform for combining the different types of data. Specifically, the unique ID of any map element will be “king”, the atomic bond between tables of attribute data, catalogs of bibliographic citations, and indexes of full-text publications. An example will make this clearer. As our drawing (failingly) attempts to illustrate, an individual map element, in this case the polygon of a house in Pompeii, will have descriptive information attached to it. The most important of these will be the name of the house, or rather the many names given a house over the centuries since its excavation. These names and their addresses will provide the handle for our processing of full text documents, allowing us to not only make the documents discoverable via the map, but also make the map serve to illustrate bibliographic searches.

Connecting citations to to places will require a number of approaches to be employed. As a proof of concept, in 2011 the PBMP first used the spatial index created by Garcia y Garcia in for his first two volumes of the Nova Bibliotheca Pompeiana. An updated version is available online. This index specifically lists each citation number associated with a particular address in the city. As the effort of one dedicated scholar, this index is truly remarkable. As a bridge between Pompeii’s physical and publication landscapes, however, it reaches less than one quarter of the way across the gulf that divides them. That is, only about 25% of all the citations are given an address and only about the same percentage of the places in Pompeii are listed. To associate more works, and to parse their contents more precisely, the PBMP is applying natural language processing techniques to all the full-text documents we can capture. Let me echo our call for help again here to grow our repository. Our authority list of Pompeii’s toponymy has been generated from its complete enumeration (more than 5000 entries) in volume II of the Corpus Topogrpahicum Pompeiana while the collocation (and implicit disambiguation) comes from the “Numerical Index” of the same volume. Because gathering the entire corpus of Pompeian scholarship in full-text will take some time, we plan to move forward with intermediate steps including parsing title keywords, processing book indexes, and seeking community help in tagging works they have read (or written!).

The Future. 

Careful viewers will have seen some notations in the image above about the future, especially concerning ways to extend the project and the multiple platforms for potential dissemination. We have always intended to have both download and upload capabilities; the ability for users to pull down our data and for the PBMP to ingest their additions, changes, and improvements. Since the project was conceived, a number of online platforms, resources, and coding practices have risen to prominence including OpenJumpPostGIS, GeoJSON, and GitHub. It is our intension to keep the doors of our data open to these and future developments.

– EP