Columbia subject headings:
Harvard subject headings:
Crop yields--Maps.
Crop yields--Statistical methods.
Food crops--Geographical distribution--Maps.
Food crops--Statistical methods.
Grain--Geographical distribution--Maps.
Grain--Statistical methods.
Princeton subject headings:
Crop yields--Maps.
Crop yields--Statistical methods.
Food crops--Geographical distribution--Maps.
Food crops--Statistical methods.
Grain--Geographical distribution--Maps.
Grain--Statistical methods.