View
30
Download
6
Category
Tags:
Preview:
DESCRIPTION
Leif Isaksen Oxford Archaeology. Ptolemy's Error: Truths and falsehoods in heterogeneous spatial data. Ptolemy's World Map. Spatial or textual Data and representation separate – catalogue and instructions Much less potential for error (perhaps) But what about his data quality?. - PowerPoint PPT Presentation
Citation preview
Ptolemy's Error:Truths and falsehoods in
heterogeneous spatial data
Leif IsaksenOxford Archaeology
Ptolemy's World Map
Spatial or textual Data and
representation separate – catalogue and instructions
Much less potential for error (perhaps)
But what about his data quality?
Ptolemy's Error
Uses 12ths of a degree
But distribution uneven
We know that the source data has varying precision
Problem – we don't know which.
Cautionary Tales
Misconception of point/area data even at standards level
Part of the problem is an oversimplified division – points/lines/polygons or vector vs. raster.
TQ125127
TQ1212
The Nature of Historic Mapping
Core Components Spatial Framework Entities (points/lines/polygons/cells)
Maps of the Past Descriptive Data underdetermines basis of compilation
Truth-standard can be defined as several 'facets' Strong and weak form Simple schema
The Categories
Incomplete vs. Complete
Fuzzy vs. Hard
Durée vs. Snapshot
Marker vs. Depiction
Observed vs. Derived
Incomplete vs. Complete
Incomplete F iff non-existent entity represented
Complete F iff non-existent entity represented or existent
entity represented Notes
Even vs. Uneven as special case
Fuzzy vs. Hard
Fuzzy Vagueness or Imprecision Vagueness F iff entities which can only be one
category are represented as another Imprecision F iff entity represented outwith
boundary of that imprecision Hard
F iff entity incorrectly categorised, or boundary condition doesn't hold
Durée vs. Snapshot
Durée F iff not all entities exist within a specified timeframe
Snapshot F iff not all entities are temporally coexistent at
specified timepoint Notes
Maps of the present are special case of Snapshots
Marker vs. Depiction
Marker F iff Marker location inaccurate with reference to
spatial framework Depiction
F iff location inaccurate or entity's and object's spatial features don't coincide
Observed vs. Derived
Observed F iff entity does not correspond to real object
Derived F iff output doesn't correspond to:
function(basedata) Notes
For Derived to have meaning, both function and basedata need to be referenced.
Questions
Theoretical Are these facets orthogonal? Periodic table - Are all combinations permissible? Interoperability - Are all combinations of
combinations useful? Practical
How can we make these facets transparent? What potential might they have for supporting data
management? Hard cases?
Recommended