topic Re: Question regarding celll data type (for university exam) in ArcGIS Pro Questions

Question regarding celll data type (for university exam)

DanielMortensen — Mon, 27 Feb 2023 11:29:04 GMT

Im having some trouble of how to calculate the following question, and would appreciate any help on how to calculate it

A raster layer is 1 Mb big and consists of 1000 columns and 1000 rows of 30 m
spatial cell resolution. What data type is the cell values stored in and describe which
values that can be stored with this data type

Re: Question regarding celll data type (for university exam)

DavidPike — Mon, 27 Feb 2023 12:27:25 GMT

I think it's leading you to say 'byte' from the filesize (i.e. 1 million cells of 1 byte each). Integer values 0 to 255 unsigned or -128 to 127 signed.

Re: Question regarding celll data type (for university exam)

JohannesLindner — Mon, 27 Feb 2023 12:41:02 GMT

1 Mb / 1000 rows / 1000 columns = 0.000001 Mb / Cell

0.000001 Mb = 1 Byte

In 1 Byte (8 bit) of data you can store one of 256 (2^8) integer values (0 ... 255 or -128 ... 127).

Of course, that's the size for the pure raster cell values. In a "real" raster format (say ESRI's ASCII raster format), you would have separators between the values in one row (space), separators between the rows (linebreak), and header data (cell size, start coordinates), so the raster size would be somewhat above 1 Mb.

Re: Question regarding celll data type (for university exam)

JohnWatt — Tue, 28 Feb 2023 03:58:46 GMT

Yip, a million bytes, one byte (8 bits) per cell, irrespective of how geographically big that cell is - so not much room there. Only 255 unique values can be stored. So maybe an index for a lookup classification, or maybe a greyscale image like a hillshade. Or a single band from an RGB(I+) photographic image. Not a DEM - you'd typically want to store floating-point numbers at least, which take more than one byte.