This mod adds optional XML tags to:
* make an improvement require access to a bonus, in the same way that railroads require coal. The requirement may be that the bonus be accessible from the tile, from a neighboring tile, from the nearest city, from the capital, on any tile in the civilization, or any combination of these.
* make an improvement provide one or more resources, without needing to be on the corresponding bonus.
* make a feature the upgrade over time, like improvements can.
This download contains the source for the modified C++ files. Search for "gordonthewhale" to find the modified parts.
See the forum discussion at http://forums.civfanatics.com/showthread.php?t=192288
Improvement, Feature, and Resource mod - source 2016-10-05
Improvement, Feature, and Resource mod - source