Texture map of size 12800 * 12800 > NO WAY!
On today's graphics cards the maximum texture size is usually 4096 * 4096.
ATI radeon > 2048
Geforce > 4096
I guess it is possible to make a texture that big but the RAM requirements are phenominal!!!
Here are some RAM (in MegaBytes) requirements for single textures >>>
Texture Size -- 16 bit -- 24 bit -- 32 bit
1024 -- 2 -- 3 -- 4
2048 -- 8 -- 12 -- 16
4096 -- 32 -- 48 -- 64
8192 -- 128 -- 192 -- 256
16384 -- 512 -- 768 -- 1024
So your 12800 texture will use just under a GB of RAM...so forget it.
Just experiment with UV tiling or detail mapping.
Tables taken from >
http://www.vterrain.org/LargeTextures/