Where the detailed 2 m LIDAR data comes from
LIDAR is surveyed from aircraft with a laser, and measures ground height every metre or two in fine detail. Ireland has no single national LIDAR survey. InSite uses three public surveys, in this order:
- Office of Public Works (OPW): flown for flood risk mapping, so it follows rivers, floodplains and the coast.
- Transport Infrastructure Ireland (TII): corridors along national roads and rail.
- Westmeath County Council.
Together they cover roughly 30% of the country. Upland and inland areas away from rivers and main roads are the most likely to be missing.
Where none of them covers a site, InSite falls back to Copernicus GLO-30, a free global elevation model from satellite radar on a 30 m grid. It's much coarser, and it measures the top of whatever is there (trees and buildings included), not bare ground. The report always tells you which source it used.
Shaded relief, contours and LIDAR: what's the difference?
| Layer | What it is | Good for |
|---|---|---|
| Shaded relief (hillshade) | A picture of the land lit by a low sun. Shows shape, not height. | Seeing hills, valleys and ridges at a glance |
| Contour lines | Lines joining points of equal height, every 10 m | Reading slope and height across a wider area |
| LIDAR elevation | A measured height every 2 m or so | Small level changes within a site: banks, hollows, drains |
Many "terrain maps" online are shaded relief only. They look detailed, but there's no height in them to read off. If you need actual levels, you need contours or LIDAR.
How to read terrain for a site
- Which way does the land fall? Water runs from high to low ground, at right angles to the contour lines. That's where surface water from the site goes, and where a soakaway or percolation area would drain towards.
- How steep is it? Count the contours: 10 m of height across 100 m of ground is a 1 in 10 slope. Steep sites cost more to build on, and affect access, drainage and how a house sits in the landscape.
- Is the site in a hollow? Low ground surrounded by higher ground can collect water. Check the OPW flood maps as well (the InSite report includes them).
- Read the colours within one map only. Each detailed elevation map is coloured from its own lowest to its own highest point, so small differences stand out. The same colour on two different sites doesn't mean the same height; the legend does.
What it can't tell you
- It isn't a topographic survey. For a planning application or a house design you'll still need levels from a surveyor.
- LIDAR shows the ground as it was on the day it was flown. Recent earthworks, new roads or buildings may be missing.
- Satellite elevation (where there's no LIDAR) includes trees and buildings, so woodland and towns read higher than the ground beneath them.
Sources
- LIDAR: Office of Public Works, Transport Infrastructure Ireland and Westmeath County Council, via Geological Survey Ireland's LIDAR coverage service.
- Contours: EPA and Geological Survey Ireland, Hydrologically Corrected Digital Terrain Model (20 m grid, 10 m contours).
- Satellite elevation: Copernicus GLO-30 Digital Elevation Model, provided under the Copernicus programme by the European Union and ESA.
Last reviewed 2026-10-02.