What is a .ASC file?
The .asc extension covers Esri ASCII grids, PGP armored data and plain ASCII text.
Esri ASCII grid
- What it is
- An Esri ASCII raster grid - a small header (ncols, nrows, cellsize) followed by a grid of elevation or raster values. Analyser reads the grid header and bounds.
- How to tell it apart
- An Esri grid starts with the word ncols.
- Did you know
- The Esri ASCII grid is so simple - a tiny header then a wall of numbers - that it became the lowest-common-denominator way to swap elevation and raster data.
- Writing every cell out as text makes the grid far bigger and slower to read than its binary equivalent, so it is used for exchange rather than everyday storage.
- GDAL knows the format as its AAIGrid driver, which is how QGIS and countless other GIS tools open the plain-text grid directly.
PGP armored data
- What it is
- An ASCII-armored OpenPGP block - a Base64-wrapped key, message or signature. Analyser reads the armor type and walks the packet structure.
- How to tell it apart
- PGP armor starts with -----BEGIN PGP.
- Did you know
- ASCII armor wraps a binary key in Base64 so it survives being pasted into email, and the trailing line starting with = is a checksum that catches copy-paste corruption.
- That final checksum is a 24-bit CRC defined by the OpenPGP standard (RFC 4880), and it guards only against accidental corruption, never against deliberate tampering.
- PGP itself was written by Phil Zimmermann in 1991, and its spread as strong crypto triggered a US criminal export investigation that was finally dropped in 1996.
Plain ASCII text
- What it is
- A plain ASCII text file. Analyser opens it as text.
- How to tell it apart
- Anything else with a .asc extension is treated as plain text.
- Did you know
- ASCII fixed the English alphabet into 7 bits in 1963, and modern UTF-8's first 128 characters still match it exactly.
- ASCII spends 33 of its codes on non-printing control characters such as carriage return and escape, a legacy of the teleprinters it was first designed to drive.
- Bob Bemer, nicknamed the father of ASCII, pushed for the backslash and escape characters and later became an early campaigner about the Year 2000 date problem.
- Depth of analysis
- .ASC is an identification-grade format: Analyser recognises it from its bytes and decodes the header metadata it carries, rather than opening it in a full viewer. Formats that do get a full viewer are marked "Full" on the formats page.
- Open a .ASC file
- Drag a .ASC file onto the Analyser home page (or tap to pick one). It is identified entirely in your browser - nothing is uploaded, there is no account, and it works offline once installed.