You can search statistical data on every fields by prefecture, which you have to  group together from huge collection of books and microfilms without this database.
For example, you can easily get the data like following:

- Transition of rice production by prefecture in Meiji period
- Number of teachers of a certain prefecture by sex and age in prewar period

[Contents]
0.9 million images, 1.5 million records of Prefectural Documents on Statistics (1873-1972)
 

[Prefectural Documents on Statistics]
Every prefecture published its statistics on population, agriculture, industrials and other fields every year from Meiji period.
It began as "Ichiran-hyo"(list) in 1873 or 1874, was standardized the data format in 1884, and continued to be published until 1941 or 1942. After the World War II, it was revived from 1947 or 1948.
Compared to national statistics, its contents were more segmentalized. Moreover, some of them were listed only in a prefectural documents.
They are the most exhaustive statistical resources on the history of Japan between Meiji and Post-War showa.