PDF Maps

An Android app for reading PDF maps — transit networks, bike path networks, anything diagrammatic. Import a PDF, pick it from an alphabetical list, zoom and pan.

These maps are diagrams, not survey sheets, so the app assumes nothing about scale or geography: no GPS, no georeferencing, no accounts. Just the map, as large as you want it.

Install

Grab the APK from the latest release and open it on your phone. Android will ask you to allow installing from unknown sources, since this is not distributed through the Play Store.

Requires Android 8.0 (API 26) or newer.

What it does

• Import — share or "open with" any PDF, or tap + to pick one. The file is copied into app-private storage, so the library is unaffected by the original being moved or deleted.
• One entry per page — a 3-page PDF becomes 3 maps, named Something (1/3) … (3/3). Single-page PDFs get no suffix.
• Library — favourites pinned on top, alphabetical within each group, with thumbnails. Long-press a row, or use its overflow button, to rename, favourite or delete.
• Viewer — pinch, pan and double-tap. Double tapping eases through two zoom stops, 3x then 6x, before returning to fit. Tiles are re-rendered from the PDF at the current zoom level, so text stays sharp all the way in to the 24x limit. Zoom and position are remembered per map.

Building

Requires JDK 17 and the Android SDK (platform 35).

export JAVA_HOME=$(/usr/libexec/java_home -v 17)
./gradlew assembleDebug

The APK lands in app/build/outputs/apk/debug/app-debug.apk. Install it with adb install -r <that path>.

local.properties points at the SDK and is not committed; create it with sdk.dir=/path/to/Android/sdk if Android Studio hasn't.

How the viewer works

PdfRenderer is not thread-safe and allows one open page at a time, so PdfDocumentSource funnels every render through a single mutex on a background dispatcher. Getting this wrong produces crashes that only appear under fast panning.

TileRenderer addresses tiles by zoom level (level N renders at 2^N times fit-to-screen scale) rather than by continuous scale, so panning at a steady zoom reuses cached tiles. Level 0 tiles are drawn underneath as an underlay, so zooming never shows blank space while sharper tiles are still rendering, and the next-coarser level is drawn between the two wherever it is still cached. TileCache is an LRU bounded to a quarter of the device's heap budget.

Layout

data/     Room entity, DAO, database, file store, repository, import
render/   PdfDocumentSource, TileRenderer, TileCache, thumbnails
ui/       LibraryScreen, MapViewerScreen, view models, theme

Not included

Search, manual rotation, inverted/dark rendering, keep-screen-awake, image formats other than PDF, anything GPS.