old thread and one that is in need of updating , maybe start a new one ?

but in the meantime ....

it really comes down to WHAT one is doing and what TYPE of "map" one is making

with that in mind , I start with a 32 bit floating point image or a 16bit Unsigned image
i find that when working on a 16 bit image that unsigned ( 0-65538 ) works better in most software than using a signed image ( -32768 to 32767 )
and move that data into 32 bit float .

this reduces the software that can be used

Also most of the work on said maps tends to be in "Simple cylindrical" for a full planet
Mercator for the areas around 45 to 85 north/south
Polarstereographic for the two poles

so for my needs the "best software" is different than someone making a dungeon

ISIS3 ( yes it is mainly for THIS solar system and NOT the Earth )
USGS Isis: Planetary Image Processing Software

GDAL
GDAL: GDAL - Geospatial Data Abstraction Library

this has many variants like FW-tools that include Proj4
FWTools: Open Source GIS/RS Binary Kit

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For viewing and over all image editing there is Nip2/Vips
VipsWiki

it is like a cross of lotas123 and gimp
the GUI " nip2" to the VIPS imaging library works a bit like a spread sheet
BUT
it handles 8 bit ( signed and unsigned)
16 bit ( signed and unsigned)
32 bit long and double
32 bit float
image data

there is also for working on 32bit images
16 bit can be done with imagemagick Q16
BUT
This has REPLACED IM as a tool i use

"G'Mic"
G'MIC - GREYC's Magic for Image Computing: An Open and Full-Featured Framework for Image Processing

as above it also handles images these forms
bool | uchar | char | ushort | short | uint | int | ulong | long | float | double
( but you need to hack the current source code to RE ENABLE some of the little used formats )

you can also use gmic's math functions to run a polar transform on a map to work on the north/south poles


there is also Gimp 2.8 is still 8 bit
sometime soon ??? Gimp3 will be out and that will handle 16 bit and i think 32 bit images