From the etymology, I would assume it means just the native sitting in/on the national land.
Means: no foreign mercenaries were accepted for this new corps,
Land-wehr literally means land defense.
Land-s-er comes from, I believe Land + the euphonic sound "s" + the suffix "er" which here means a man: so the original meaning was; (fellow) countryman, later: a German soldier.
"Landser" appears in the German language as late as the 20th century, I am very sure it was not in use during the Napoleoinc wars.
Yes, indeed, but, if I understand correctly, the component land, which those word have in common, relates to both 'the nation' and to physical territory, or even a given locality. If so, it seems the meaning of landzat seems to relate to the authorities' tapping into a local resource to bolster the static defences of Gelderland and Utrecht, where the main French attack was likely to fall. They were looking for local recruits to provide supplementary manpower for the artillery batteries being built in their districts, along the Rhine and on the Heights of Greb.
Smart uniforms, good pay and remaining in the home area, contributing to its defence, offered a counter to the general disaffection which had spread to the national regiments in the States regular army, where leadership was poor, morale was low, and there was little enthusiasm for shoreing up the rule of the House of Orange.
Landzat would seem to be an archaic term now, although in historical writing, the spelling has nonetheless been modernized from landzaat to landzat. What I am still not clear about is whether this was a traditional military label in 1794 or whether it was a new term invented for new circumstances, but that is not especially important.
Anyway, thank you, Oliver. That has been very helpful and most interesting.