How to open a KMZ file
Updated 27 September 2026
A KMZ is a ZIP archive that holds a KML document and the icons it uses. Google Earth, QGIS and OpnEarth all open one. Large files are the hard part. A KMZ compresses about 11:1, so a 15 MB file can hold 160 MB of XML, and many viewers plan for the smaller number.
Why a large KMZ is slow to open
The size on disk is the compressed size. The viewer has to read the expanded KML. These figures come from Canada's public ISED National Broadband Internet Service Map:
Public open data, published by Innovation, Science and Economic Development Canada. Measured by OpnEarth on the published file.
A program that sizes its work from the 15 MB figure underestimates it about tenfold. The download takes seconds, and then the drawing can take minutes or stop partway.
Ways to open one
- A small file you open now and then. Google Earth Web opens a KMZ in a browser tab. It uploads the file to do so, so avoid it for confidential data.
- A large file on a Mac. Google is ending Google Earth Pro on macOS. Use a current desktop viewer that handles large files, such as OpnEarth.
- You need to reproject or run analysis. Use QGIS. It imports KML. Expect to set a coordinate reference system and restyle the layers, because the sender's KML styling does not carry over fully. For buffers, distance searches or MTM and UTM coordinates on their own, OpnEarth has them built in.
- You want to read it and send it on. Drag it into OpnEarth. It opens with the sender's styling and folders, and the file stays on your computer.
Opening a KMZ in OpnEarth
- Start OpnEarth.
- Drag the
.kmzor.kmlfile onto the window. You can also choose Open file on the start screen, or press Ctrl+O (⌘+O on a Mac). - The file's folders appear in the layer list on the left. Tick or untick a folder to show or hide what it contains.
The free Lite edition has no edition-based size cap for local desktop files. See how to install it and the system requirements.
Once it is open
Opening the file is usually the first step. These are the questions that come next, and where OpnEarth answers them:
- How long is it? Measure a distance or an area, or right-click a line and choose Elevation profile. Both are in the free Lite edition.
- What is near this route? Right-click a layer and choose Find within distance… to select everything within, say, 50 m of it, save it as a folder or create a buffer.
- How many kilometres per owner? In Pro, Totals by… gives the count, length and area for each value of any field, ready for Excel.
- What changed since the last version? In Pro, right-click the file and choose Compare with another version… to see what was added, removed and changed, even when the file has no IDs.
- How do I pass it on? In Pro, share a web link that keeps the map's colours, or make a PDF map book with one page per route.
How the options handle a large KMZ
| OpnEarth | Google Earth Pro | Google Earth Web | QGIS | |
|---|---|---|---|---|
| Platform in 2026 | macOS and Windows | Ending on macOS | Browser only | Native |
| Large vendor KMZ | Built for it | Minutes, or a stall | 250,000 vertex cap | 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 |
This compares the task of opening a KMZ that somebody emailed you.
KMZ or KML?
KML is the XML text. A KMZ is that XML zipped together with its icons and overlays in one file. Both are open formats standardised by the Open Geospatial Consortium, so any program can implement them and 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 makes the file small enough to email.
Why is my KMZ so slow to open?
The viewer has to parse the expanded KML. A KMZ compresses roughly 11:1, so a 15 MB attachment can expand to 160 MB of XML. A viewer that plans for 15 MB runs short when it meets 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 on macOS and Windows.
Is there a file-size limit?
OpnEarth has no edition-based size cap for local desktop files on any plan, including the free one.
Do I need to be online?
No. A local KMZ opens with the network off, and the file stays on your computer.
What happened to Google Earth Pro on macOS?
Google is ending Google Earth Pro on macOS. Your files are unaffected. KML and KMZ are open formats, and any viewer that implements them can read them.