How to open a KMZ file
Updated 6 September 2026
A KMZ is a ZIP archive holding a KML document and the icons it references. Any KML viewer opens one: Google Earth, QGIS, or a dedicated viewer. Large ones are the problem. A KMZ compresses about 11:1, so a 15 MB file can be 160 MB of XML, and most viewers judge it by the smaller number.
Compressed size is a lie
This is the whole difficulty. A KMZ that arrives as a 15 MB email attachment is not a 15 MB file. Measured on Canada's public ISED National Broadband Internet Service Map:
Public open data, published by Innovation, Science and Economic
Development Canada. The full profile ships with the OpnEarth source as
docs/fixtures/0001-ised-broadband-canada.md.
Any check that asks "is this file big?" by looking at the size on disk gets the answer wrong by an order of magnitude. That is why a file that downloads in seconds can then take minutes to draw, or never finish.
Opening one
- Small file, occasional use. Google Earth Web opens a KMZ in a browser tab. It uploads the file to do it, which rules it out for anything confidential.
- Large file, on a Mac. Earth Pro's support on macOS has ended. A native viewer built for the size is the remaining option.
- You need to edit or reproject. QGIS. It imports KML, but expect to set a CRS and restyle, because the sender's KML styling does not survive the trip intact.
- You just need to read it and pass it on. Drag it into OpnEarth. No import step, no projection dialog, and the file stays on your machine.
What each option does with a large KMZ
| OpnEarth | Earth Pro | Earth Web | QGIS | |
|---|---|---|---|---|
| Platform in 2026 | macOS, Windows, Linux | Ending on macOS | Browser only | Native |
| Large vendor KMZ | Built for it | Minutes, or a stall | Chokes | Slow import |
| Steps to first view | Drag it in | Drag it in | Upload and wait | Import, CRS, restyle |
| Keeps the sender's styling | Yes | Yes | Partly | Needs restyling |
| Works offline | Yes | Partly | No | Yes |
| File leaves your machine | No | No | Yes, on upload | No |
Describes the "open a KMZ someone emailed me" task. OpnEarth is a viewer, not a GIS: geoprocessing and projection work are what QGIS is for.
KMZ or KML?
KML is the XML. KMZ is that XML zipped together with its icons and overlays, under a single file extension. Both are open formats standardised by the Open Geospatial Consortium, so no single vendor controls whether your files stay readable.
Questions
What is a KMZ file?
A KMZ is a ZIP archive containing a KML document and the icons and overlays it references. KML is the XML that describes the placemarks, polygons and styling; zipping it is what makes the file small enough to email.
Why is my KMZ so slow to open?
Because the size on disk is not the size being parsed. A KMZ compresses roughly 11:1, so a 15 MB attachment can expand to 160 MB of XML. Viewers that judge the file by its compressed size allocate for 15 MB and then meet ten times that.
Can I open a KMZ without Google Earth?
Yes. KML and KMZ are open formats published as an OGC standard, so any viewer can implement them. OpnEarth opens them natively on macOS, Windows and Linux.
Is there a file-size limit?
Not in OpnEarth, on any plan including the free one. Opening a large file is not paywalled.
Do I need to be online?
No. A local KMZ opens with the network off, and the file never leaves the machine.
What happened to Google Earth Pro on macOS?
Google has ended support for Earth Pro on macOS. The files are unaffected: KML and KMZ are open formats and any viewer that implements them can read them.