The short version: LAZ is a losslessly compressed LAS file. Same points, same attributes, same coordinate reference system, roughly a tenth of the bytes. Because nothing is discarded, the decision is not about data quality — it is only about whether your tools can read compressed input, and whether you would rather spend disk space or CPU cycles.
Side by side
| LAS | LAZ | |
|---|---|---|
| File size | Baseline | ~10–20% of LAS |
| Data fidelity | Full | Full — lossless |
| Read cost | None | Decompression on the fly |
| Random access | Direct | Per chunk |
| Software support | Universal | Broad, but not universal |
| Open standard | Yes (ASPRS) | Yes (LASzip) |
| Best for | Active processing, older tools | Storage, archiving, transfer |
How much smaller, really
LASzip is commonly cited as producing files 7 to 20 percent of the original size. The variation is not random — it tracks how compressible your particular data is:
- Compresses well: dense aerial survey data with regular scan patterns, where consecutive points differ by very little.
- Compresses less well: sparse or irregular clouds, and files whose header scale factors demand high coordinate precision, since the low-order bits are closer to random.
- Barely matters: the number of populated attributes. Empty or constant fields cost almost nothing either way.
Choosing
Use LAZ for anything at rest: archives, deliverables, data you are sending to a client, anything in cloud storage where you pay per gigabyte. There is no integrity reason to prefer LAS, and LAZ is an open format with several independent implementations, so compressing does not lock your data to a vendor.
Use LAS when a tool in your chain will not read compressed input — older QGIS builds, ArcMap, several CAD import paths — or when you are about to read the same file repeatedly in a tight loop and the per-read decompression cost starts to add up. A reasonable pattern is to keep a working LAS for the duration of a project and archive the LAZ.
Where COPC fits
COPC (Cloud Optimized Point Cloud, .copc.laz) is a LAZ file reorganised into a spatial octree with an index, so a client can fetch just the region and detail level it needs over HTTP without downloading the whole file. The compression is identical — it is a layout change, aimed at web and cloud delivery. It complements LAZ rather than replacing it: LAZ for archiving, COPC for serving.
Converting between them
Conversion is lossless in both directions, so it is safe to move back and forth as your workflow needs. Decompress LAZ to LAS or compress LAS to LAZ in your browser — no upload, no size limit, and the coordinate reference system is preserved.