Data quality in spatial databases has been widely recognized as one of the most critical issues in GIS. Its key dimension is assessing data suitability

including data accuracy

precision

uncertainty

compatibility

consistency

completeness

availability and timeliness recorded in the data lineage. Over decades

data quality has attracted much attention in the GIS community

and various aspects of data quality have been investigated. However

research on topological consistency remains very weak though it is crucial for GIS spatial analysis. This paper proposes a new technique on handling topological consistencies as well as tracing error propagation. First

inconsistencies of digital geographic lines are categorized into two groups with or without equal numbers of vertexes. Then a standard formalizing approach has been introduced to make numbers of vertexes matched in the two poly-lines so that the generalized algorithm of node snapping can be used to remove the inconsistencies between the two poly-lines. Third

the equations of estimating the coordinates of the projected points and their errors in the process of standard formalization have been derived. The formulae of calculating the length

together with its accuracy

of new generated poly-lines have also been obtained. Finally

simple examples are provided to demonstrate how to implement the proposed technique into practice.