Trying to add a property from an attribute table to a raster data in QGIS possible

Question

I am really new to GIS in general. I've been working with QGIS.

I downloaded this data: WISE30sec Soil Properties. I'm trying to create a geotiff clipped to my study region with the soil property's TAWC(total water available capacity) value from the attribute table in the zip file for each grid cell of the raster file.

I followed the instructions in the zip file:

Using ArcGIS or similar, user may join the raster data to the derived soil properties files, as managed the MSAccess database (WISE30sec.mdb). Linkage is through the map unit code or grid cell identifier(NEWSUID) of the raster set and the NEWSUID of the various soil attribute data files.

I managed to connect the MSAccess database in QGIS and get the attribute table, but I cannot find a way to add properties from the table with the NEWSUID grid cell identifier to the raster map. All I've found online are tutorials on how to add attributes to a vector layer and not to a raster layer.

Is it even possible in QGIS? Or maybe I misunderstood the instructions.

Edit: Complete Instructions from the ReadME file in the zip file:

This soil data set is provided in one single zip file, called WISE30sec_v1.zip. By default, this fill will be unzipped to folder X:\WISE30sec, where X is the actual folder on your system.

The zip file includes a raster GIS file(WISE30sec) as well as a range of soil attribute data files; for details please see Appendix 3 in the technical documentation.

Using ArcMap, users may join the raster data to the derived soil properties files, as managed in the MSAccess database (WISE30sec.mdb). Linkage is through the map unit code or grid cell identifier (NEWSUID) of the raster set and NEWSUID of the various soil attribute data files. The above files are also provided in TIFF and TXT format ( see folder "...\interchangeable_format") so that they may be easily accessed using other systems.

Depending on the proposed applications, users may select the appropriate data set(s) with due consideration for the issues raised in Section 3.4 in the technical report on "appropriate use of the derived data': comprehensive studies should consider the full mapping unit composition.

Answer 1

The concept of raster data does not include attributes. Only vector data have attributes in the sens you think of. Raster data include raster-values that can represent different things like elevation, vegetation-type, amount of precipitation and so on on a pixel per pixel approach: each pixel contains a value: be it in a single-band with just one value - from black to white, be in a multiband with different values for each color-band (e.g. remote-sensing images orthophotos). So you simply can't add attributes to pixels - and pixels is what your raster basically consists of. So you should reconsider your approch, e.g. by converting your raster to a vector data-type.