Introduction

This chapter examines the different ways in which spatial datasets are acquired and structured to take advantage of the visualisation and analytical abilities of GIS. It is conventional to distinguish between primary and secondary data sources because acquisition methods, data formats and structuring processes differ considerably between the two. Primary data consist of measurements or information collected from field observations, survey, excavation and remote sensing. Secondary data refer to information that has already been processed and interpreted, available most often as paper or digital maps. Many users of GIS wish to integrate primary and secondary datasets (for example, to plot the location of primary survey data across an elevation model obtained from a data supplier). Both types of data have advantages and disadvantages, which this chapter examines in some detail. By the end of this chapter you will be familiar with the ways in which both primary and secondary data are obtained, and the issues and procedures for assessing the quality of combined datasets.

Primary geospatial data

Primary, or ‘raw’, geospatial data has not been significantly processed or transformed since the information was first captured. Archaeologists generate vast quantities of primary data during excavation and survey, such as the location of settlements, features and artefacts, geoarchaeological and palaeo-environmental data and the location of raw material sources within the landscape. Raw data may also be available from databases of information compiled by other agencies: the location of archaeological sites, for example, can be obtained from Sites and Monuments Records and published site ‘gazetteers’.