An information processing system includes a server and a first vehicle acquiring a combination of first and second position information of the first vehicle. The first position information is calculated using a positioning signal from the first satellite system. The second position information is obtained by correcting an error of the first position information using a positioning reinforcement signal from the second satellite system. The first vehicle or the server calculates difference information between the first and second position information for each combination thereof. The server estimates a calculation accuracy for the first position information in a road section on a road map based on one or more pieces of difference information in which one or more positions indicated by the second position information corresponding to the difference information are within the road section and to output the calculation accuracy for the first position information in the road section.