$ cd ~/apps
// ~/sounder

Sounder

A field map for iPhone: trails and two-tracks, back forties, rivers and marshes. Stack as many maps as you want, fade one over another, record where you went, and add your own layers from the open formats everyone already publishes in.

get it on the App Store

Sounder's icon: contours running from green upland down into blue depth bands, with a blaze-orange pin on the bank
$ cat features.txt
  • A stack of maps. USGS topo, imagery and relief, NWS radar, NOAA charts, Corps of Engineers river charts, Forest Service road maps. Turn on any number; the bottom one is the base, and each layer above it has its own opacity.
  • Your own layers. ArcGIS map and image services, WMS, XYZ and TMS tiles, TileJSON, MBTiles and PMTiles, from a URL or a file. What you can connect, and where to find it.
  • Catalogs. A JSON file anyone can host that lists layers and offline packs. Subscribe once and new layers show up on their own.
  • Tracks and waypoints. Record with the screen off, mark spots with icons, notes and photos, draw areas. Import GPX, KML and GeoJSON; export GPX.
  • Offline. Frame an area on the map and download it, layers and all. Offline packs and tile files work with no signal too.
  • Backed up. Everything you save goes to your own iCloud Drive, with 30 days of daily snapshots and a GPX copy any app can read.
  • No account, no ads, no tracking.
$ cat faq.txt
How do I add a map?
Layers, then Add Layers. Add from URL takes the address of an ArcGIS map or image service, a WMS, a tile template with {z}/{x}/{y}, a TileJSON or PMTiles URL, or a catalog. Import file takes MBTiles, PMTiles, GPX, KML, KMZ and GeoJSON. You can also open any of those from the Files app. The map sources guide has examples you can add with one tap.
How do I switch base maps?
Turn on as many as you like. The lowest active layer is the base; drag to reorder and use each layer's slider to fade it over the ones below.
Where are my backups?
Files, iCloud Drive, Sounder. Settings shows when the last one ran and can restore any of the last 30 days. Offline packs aren't backed up; they download again.
Coming from another app?
Export GPX or GeoJSON from it and open the files in Sounder. GeoJSON exports that carry ids keep them, so importing a newer export later only adds what's new.
Can I trust the depths and boundaries?
Not blindly. Map data comes from public agencies and from sources you add, and it can be out of date or wrong: river surveys age, channels move, and tax-roll ownership can be mistaken. Use it alongside official charts, posted signs and your own judgment.
$ mail # bugs, ideas, a layer that won't load

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$ cat CREDITS

Maps by MapLibre Native (BSD). Built-in layers from the U.S. Geological Survey (The National Map, 3DEP), NOAA Office of Coast Survey, the National Weather Service, the U.S. Army Corps of Engineers (Inland ENC) and the USDA Forest Service, all public domain. Fonts: Open Sans (Apache 2.0).