The definition of a desk-based assessment given by the Chartered Institute for Archaeologists (CiFA) in The Standard and Guidance for Archaeological Desk-Based Assessment is:

Desk-based assessment is a programme of study of the historic environment within a specified area or site on land, the inter-tidal zone or underwater that addresses agreed research and/or conservation objectives. It consists of an analysis of existing written, graphic, photographic and electronic information in order to identify the likely heritage assets, their interests and significance and the character of the study area, including appropriate consideration of the settings of heritage assets and, in England, the nature, extent and quality
of the known or potential archaeological, historic, architectural and artistic interest. Significance is to be judged in a local, regional, national or international context as appropriate.

Desk-based assessments are commonly required by the local authority as part of the planning process providing a valuable insight into any heritage issues that may arise in any proposed development site.

The scope of any requested desk-based assessment will be defined by the local authority in the form of a planning condition, written specification or project design.