Archaeological GIS

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Lecture 01 : Introduction to GIS (link to Powerpoint file)

GIS in Archaeology: Introduction to GIS

What is GIS? A Geographic Information System is a system for capturing, storing, querying, analyzing and displaying geographically referenced data.

Related Computer Programs:

Graphic “paint” programs Can make graphic displays

Computer Aided Design (CAD) programs Can split data into separate groups to make graphics Computer Aided Mapping (CAM) programs Can contain information on the actual geographic locations of objects

Computerized database programs Can manage large amounts of information that can be linked to describe and understand and entity

Components of a GIS Enterprise:

Computer hardware

Computer software

Brainware (aka humans)

Infrastructure

GIS Data Organization

GIS programs allow the user to store data in separate files and then merge these data. Data are stored as a series of thematic layers. Thematic layers can be combined to create a map or for analysis purposes.

What constitutes Geographic Data?

Spatial Data Contains the information that locates a feature in geographic space. For an archaeological site the spatial data could be the UTM coordinates of the center of the site, or it could be the UTM coordinates that define the perimeter of the site. Attribute Data Contains the characteristics that define and describe a feature. For an archaeological site attribute data would likely include the name, size, artifact density, etc.

Basic Types of Spatial Geographic Data:

Discrete data: Discrete geographic data exists in fixed locations that we classify as being internally homogeneous Examples of discrete data would be rivers, roads, archaeological sites, etc.

Continuous data Continuous geographic data is data which keeps varying over geographic space Examples of continuous data are elevation, soil moisture, Ph. concentrations, etc.

GIS Representations of Discrete Data

Discrete data are generally stored as “vector” data. There are 3 common basic vector data types: points, lines, and polygons .

GIS Representations of Continuous Data

Continuous data are generally stored as “raster” data. Raster data techniques divide up geographic space into a grid of equal sized data cells.

Common Types of Raster Data

Scanned paper maps

Digital Aerial Photographs (a.k.a. Digital Ortho Quads)

Multispectral Satellite Imagery

Digital Elevation Models (DEM)

Raster vs. Vector Data Format

Vector formats map data by storing the spatial coordinates that define individual entities (e.g. archaeological sites, streets, soil units). Raster formats map data by dividing space up into equal sized grids and then code each cell with the appropriate value.

Organization of Attribute Data

GIS attribute data are typically stored in tables. Table data are stored in columns (fields) and rows (records).

Attribute data for a feature can be stored in one table or split over multiple tables

Joining vector data spatial & attribute information

The standard GIS approach splits the spatial and attribute data into separate files. GIS links these files by storing an internal key identifier in the different files. This is the same basic principle used in relational database systems

Joining raster data spatial & attribute information

The standard GIS approach stores the raster data internally as a series of cell values. A separate small file (or header in the data file) contains the spatial extent and cell size of the data. Raster data typically contains only one or at most a few pieces of data for each location.

Basic Geographic Operations

Spatial data input

Attribute data management

Data display

Data exploration

Data analysis

GIS modeling

Spatial Data Input

GIS must have a means of inputting spatial data. Spatial data can come from a variety of sources: digitized paper sources, remotely sensed imagery (aerial photos, satellite), GPS systems

Attribute Data Management

Must be able to input new attribute data Must be able to update existing attribute data GIS must be able to link attribute data to the spatial data file

Data Display

GIS allows user to display the geographic data in various ways Maps Tables Charts Graphics

Data exploration

GIS programs provide visualization techniques to help the user understand the data Entity identification Spatial data query Geographic visualization

Data Analysis

GIS programs provide sophisticated analytic techniques to help users understand the data: Vector data analysis, Buffering, Overlay, Raster data analysis, Local measure, Zonal measures, Spatial interpolation.

GIS Modeling

GIS provide techniques to create complex models to understand data: Binary Models, Index Models, Regression Models, Process Models.