ESRI ASCII Grid (.asc)
Open BetaESRI ASCII Grid is the common text format for an ELEVATION GRID: a six-line header (NCOLS, NROWS, XLLCORNER, YLLCORNER, CELLSIZE, NODATA_VALUE) followed by space-separated numbers. Every cell value IS the elevation in METRES above sea level with one decimal — not a colour, not a shadow, not an image pixel. Heights come from the global Copernicus DEM GLO-30: about a 30 m step, vertical accuracy ~2–4 m. The grid is clipped exactly to the area you ordered, written in the coordinate system you chose, and empty cells carry NODATA_value -9999. Delivery is a ZIP holding exactly two files: map.asc and map.prj with the coordinate system (the .asc itself has nowhere to declare it). An honest caveat: over the sea GLO-30 returns exactly 0 m rather than emptiness — that is the behaviour of the elevation source, not a fault of the export. Text is bulkier than a binary raster, so the grid has a ceiling of 4 million cells: a larger area is coarsened just enough to fit, and the new step is stated as a number. It opens in a plain text editor, ArcGIS, QGIS, GRASS, GDAL, R, rasterio, Surfer and Civil 3D. This is pre-design, GIS and visualisation — not a land survey.
Caratteristiche principali
Informazioni sul formato ASCII Grid
ESRI ASCII Grid is the simplest of the raster formats: six header lines (the number of columns and rows, the coordinates of the lower left corner, the cell size, the NODATA value) and then a grid of numbers separated by spaces. The file reads in any text editor and is parsed by five lines of code in any language, which is why it is still used in academic pipelines and for long-term storage.
The format is chosen when what matters is not efficiency but portability and transparency: a supplement to an article, a dataset in a repository, an input grid for GRASS, R or rasterio, an exchange with a colleague who has no GIS. Everything in the file is visible to the eye — nothing is hidden in a binary structure.
The output is a ZIP archive with two files: map.asc with the grid of values and map.prj with the description of the coordinate system. It is done that way because the .asc itself does not store the projection, and without it a GIS will not put the grid in its place. The cells hold ELEVATIONS in metres above sea level with one decimal: a clip of the global Copernicus DEM GLO-30 exactly to the area you ordered, about a 30 m step, vertical accuracy ~2-4 m; cells without coverage get -9999. Over the sea the source returns exactly 0 m rather than emptiness — that is how it behaves, and we do not hide it.
Quale programma apre i file ASCII Grid
I seguenti programmi e applicazioni possono aprire, modificare ed elaborare i file ESRI ASCII Grid (.asc) (.asc) esportati da OSM2CDR:
Format specifications
- Open standard
- 3D coordinates supported
- Lossless (no quality loss)
- No attributes
- Output: 2 files in archive
- A ZIP with exactly two files: map.asc (six-line AAIGrid header plus cell values that ARE elevation in metres, one decimal, NODATA_value -9999) and map.prj with the coordinate system; heights from Copernicus DEM GLO-30 (~30 m cell, vertical accuracy ~2-4 m), 0 m over the sea because that is what the source returns.
Chi usa le mappe ASCII Grid
Come esportare in ASCII Grid
Come aprire il file dopo l'esportazione
- Unpack the archive — keep map.asc and map.prj in the same folder and with the same name, otherwise the GIS will not find the coordinate system.
- QGIS — Layer → Add Raster Layer → pick the .asc; the grid lands in its place, because the extent and the cell size are written in the header.
- GDAL — gdalinfo map.asc shows the header and the extent, and gdal_translate converts the grid into GeoTIFF if you need a compact binary version.
- R and Python — terra::rast() or rasterio.open() read the format directly; if you like, the grid can be loaded with plain numpy, skipping the six header lines.
- A text editor — Notepad++ or any other will open the file to check the header; for large areas pick an editor that handles big files.
Mappe popolari in ASCII Grid
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Scarica mappe ASCII Grid professionali da OpenStreetMap. Generazione istantanea, qualsiasi area.