Modern Garmin watches offer generous internal storage for onboard mapping, but preparing a watch from a Mac is surprisingly difficult. Many current Garmin models use Media Transfer Protocol (MTP) for file transfers. Unlike Windows, macOS does not natively mount MTP devices as accessible drives in Finder.
While Garmin Express handles official updates and map purchases, it provides no interface for third-party map downloads. When a runner or hiker wants to install custom terrain or regional maps, they face a frustrating barrier: the watch charges via USB, but Finder refuses to display it as a storage volume.
Resolving this typically requires third-party MTP file browsers, manual ZIP archive extraction and deep folder navigation, a technical barrier that deters many from using custom maps altogether.
Enter Terento: open-source map management for macOS
Terento is a free, open-source macOS desktop application designed to eliminate the friction between Mac computers and Garmin watches. Created by developer Gediminas, a longtime Garmin user who regularly relies on custom maps for hiking, the app consolidates browsing, downloading, extracting and transferring custom maps into a single interface.
Instead of requiring separate MTP utility programs, which are often branded for Android devices and confuse Mac owners, Terento manages the entire pipeline natively on macOS.
How Terento works
TL;DR: Terento lets Mac users find, install and manage custom third-party maps on MTP-compatible Garmin watches. It handles everything natively through a built-in catalogue or local .img files without using Finder or separate MTP file browsers.
The app presents a unified interface where watch owners can connect their device, select a map provider and transfer files directly over USB.
The complete installation workflow consists of three automated phases:
- Detection: Terento recognises connected MTP-compatible Garmin devices and checks available storage space.
- Preparation: The athlete selects a region from the internal catalogue or loads a local .img map file from the Mac, and Terento automatically downloads and extracts the archive.
- Transfer: The app writes the correctly structured .img file directly to the appropriate watch system folder and verifies transfer integrity.
Worked example: installing a 129.2 MB BBBike map on a Garmin fēnix 8
To see how Terento simplifies the workflow, consider a real-world scenario: preparing a Garmin fēnix 8 (47 mm AMOLED) for an upcoming outdoor event.
Connection and storage check: the fēnix 8 is connected to an Apple Silicon Mac via USB. Terento instantly detects the watch, reads Firmware version 23.31, and reports 15.12 GB of available storage out of 31.06 GB.
Map selection: under the Install maps tab, searching for “Lithuania” displays available options across providers. Selecting the BBBike map release shows an exact size of 129.2 MB.
Automated pipeline: clicking Continue and Install maps initiates Terento’s four-stage installation workflow.
- Downloading: pulls the map package directly to the Mac at high speed (for example, 6.8 MB/s).
- Preparing: verifies the files and prepares the Garmin image format.
- Installing: writes the validated map directly to the watch over MTP.
- Finishing: conducts final checks to ensure transfer integrity.
Verification and storage management: within moments, Terento confirms the map is ready and that the watch can be safely disconnected, leaving 14.99 GB of remaining storage. Under Manage maps, the newly installed BBBike map is clearly listed alongside its file size and one-click removal controls.
Integrations, compatibility and key features
Terento is designed as a focused, lightweight utility for endurance athletes using Apple hardware.
- Hardware and OS support: runs natively on Apple Silicon Macs (M1, M2, M3, M4) running macOS 13 (Ventura) or newer.
- Garmin watch compatibility: built for any Garmin smartwatch with onboard mapping and MTP file transfer. Terento maintains a live community compatibility log with verified successful transfers across models like the fēnix 8, fēnix 9 and Forerunner 970/955. A model’s absence from the tracker simply means an installation report hasn’t been submitted yet, not that it is unsupported.
- 1,000+ map sources: built-in direct downloads from major OpenStreetMap contributors, including BBBike, Freizeitkarte, MapRando and OpenTopoMap.
- Contour line add-ons: optional topographic contour overlays for supported OpenTopoMap regions.
- Local file import: allows manual import of custom .img map files sourced outside the built-in catalogue.
- On-device storage management: scans the watch to list installed third-party maps, showing exact file sizes and offering one-click deletion; it protects original Garmin base maps from deletion.
- Update alerts: automatically checks whether an installed catalogue map has a newer version published by the provider.
- Open source and free: distributed under an open-source license with no accounts, subscriptions or hidden paywalls.
Quick answers
Which Garmin models does Terento work with?
Terento is designed for Garmin watches with onboard maps and MTP file transfer. Community members have reported successful installations on models in the fēnix, Forerunner and epix families. The compatibility page brings those results together, but a watch does not need to appear on that page to work with Terento.
Is it safe to install third-party maps?
Terento includes checks to reduce installation risks, but those checks cannot guarantee a third-party map’s accuracy or eliminate transfer errors. Check a newly installed map on the watch before a trip.
Will a Garmin system software update delete custom maps?
No, Garmin firmware updates and official map updates do not erase custom .img files stored in the watch’s custom map directories, though keeping backups on the Mac via Terento is always recommended.
Author: Gediminas, developer of Terento, edited by the5krunner.
Last Updated on 22 September 2026 by the5krunner
My favourite kit and nutrition
- Garmin Fenix 9 Pro — I’ve just bought one.
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- Garmin 90-degree charging adapter — A small keyring adapter you can use anywhere. Essential when away. I use one.
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- Body Glide – The blue anti-chafe stick that all swimmers and many runners use. I use it.
- Maurten — The race nutrition trusted by elite athletes. Gels and drink mixes engineered to be easy on the stomach. I use them.
- Garmin Varia RTL515 — A radar rear light that alerts you to vehicles approaching from behind. Pairs with your Edge or Wahoo. I use this model.
- Favero Assioma Pro RS2 — The power-meter pedals most serious cyclists choose. Accurate, easy to move between bikes. I use this model.
- Garmin Forerunner 970 — A serious choice for a pro-grade triathlon watch. I use this.
- Polar H10 — My daily driver for accurate, waking HRV readings.
- Wahoo ELEMNT Roam 3 — The bike computer that has the feature Garmin lacks: usability. I use mine on most rides.
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tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID
