The accuracy of map overlays: A reassessment

Despite warnings in an earlier report concerning map errors, map overlay is a growing part of landscape planning, particularly as a result of developments in automated geographic information systems. Map error is unavoidable, but this previous analysis of error needs to be revised. Theoretical assessments of expected error should be combined with the results of empirical tests. Errors encountered in careful use of automated map overlay can be substantially lower than have been predicted. Experience from actual applications shows that methods of checking layers against each other produce more reliable data.