An essential wonder on large/giga maps is Marco Polo's Embassy. Give a few techs away to the AI so you can exchange maps. Once you have the geography you can direct your caravans/troops to their targets.
Giga Worlds are challenging when it comes to logistics. (Megellan is also a serious consideration) Plenty of railroads are required to ferry units to remote destinations. I usually have around 80/100 engineers at work towards the end of a giga game!
Your research goals are aimed at building efficient units:
Seafaring for Explorers
Navigation for Caravels (Megellan)
Magnetism for Galleons
Railroad for movement of land units (Darwin)
Explosives for Engineers to build the railways
Industrialisation for Transports to shuttle between "Channel Ports"
The Corporation for Freights ...and if you reach this far ... Espionage for Spies.
Leo's upgrades help!
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SG(2)