Bedrock is the solid rock at or below the land surface. Over much of Ireland, the bedrock is covered by materials such as soil and gravel. The Bedrock map shows what the land surface of Ireland would be made up of if these materials were removed. As the bedrock is commonly covered, bedrock maps are an interpretation of the available data.

Geologists map and record information on the composition and structure of rock outcrops (rock which can be seen on the land surface) and boreholes (a deep narrow round hole drilled in the ground). Areas are drawn on a map to show the distribution of rocks.

Faults are vital information that is needed alongside bedrock geology maps to provide information on the structure of rocks.

The faults show the details of the structural geology. Faults are the result of great pressure being applied to rock across a whole continent or more. These rocks will break under the pressure, forming faults. Faults are recorded as lines where the break in the rock meets the surface.

In terms of time scale in geology, Quaternary is the present-day time and it began 2.6 million years ago. A lot of this time period relates to the Ice Age.

Quaternary sediments are the soft material that has been deposited during this time. In Ireland much of this is related to the movement of glaciers and ice sheets. The main types of sediments shown on the map are tills (boulder clays), gravels, sands and peat. Over most parts of Ireland, these sediments cover the bedrock (solid rock at or below the land surface).

Geologists map and record information from the shallow sediments which can be seen at or near the surface. This information along with boreholes (a deep narrow round hole drilled in the ground), geophysical data (information on the physical properties of the Earth's surface and subsurface e.g. magnetics, gravity and electromagnetics) and geochemical data (chemical properties) is used to create the map. Areas are drawn on a map to show where sediments are found.

OneGeology-Europe is an EU project which aims to make geological data held by the geological surveys of Europe more easily discoverable and accessible via the internet. It also aims to standardise and harmonise the data in order to create an EU map.

“Geology” within OneGeology-Europe is defined as "composition (lithology/geochronology) and structure of the surface geology”.

Surface geology = geology that would be visible if the overlaying soil were removed, in other words: the Quaternary/superficial geology plus the exposed bedrock.

Lithology refers to the rock type. Geochronology refers to the age of the rock.

The Bedrock geology is defined as pre-Quaternary geology.

To produce this dataset, the Geological Survey Ireland (GSI) bedrock geology 1:500,000 and 1:100,000 maps were generalised. Standardised EU field names and codelists were used and the GSI data was mapped to the specifications.

This map is to the scale 1:1,000,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 10km.

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas).

The bedrock data is shown as polygons. Each polygon holds information on the GeologicUnit name, description, type, age, Observation Method, position accuracy, Event Environment, Event Process, Lithology, Younger and Older ages. Some values refer to defined values in the Commission for the Management and Application of Geoscience Information (CGI) vocabularies.

The surface data is shown as polygons. Each polygon holds information on the GeologicUnit name, description, type, age, Observation Method, position accuracy, Event Environment, Event Process, Lithology, Younger and Older ages. Some values refer to defined values in the Commission for the Management and Application of Geoscience Information (CGI) vocabularies.

The structural data is shown as lines. Each line holds information on the GeologicUnit name, fault type, Observation Method, position accuracy, Contact purpose and sampling frame. Some values refer to defined values in the Commission for the Management and Application of Geoscience Information (CGI) vocabularies.