1. A computer-implemented method of verifying or filling in at least one attribute associated with segments of transportation networks that are digitally mapped from a digital transportation network database, said method comprising: identifying, by a processor, an attribute of interest; identifying, by the processor, at least one segment in question of the transportation network, wherein the at least one segment in question is present in the database, but is missing the attribute of interest or for which the attribute of interest has unreliable accuracy; using, by the processor, the at least one segment in question to identify, in the database, a first segment of the transportation network and a second segment of the transportation network, wherein the first segment is immediately preceding and connected to a front end of the at least one segment in question and the second segment is immediately succeeding and connected to a back end of the at least one segment in question, and further wherein database attribute associated with the first and second segments is determined to be accurate; gathering, by the processor, a plurality of probe traces from users of probe-transmitting personal navigation devices that have traversed the at least one segment in question as well as traversed the first and second segments on either side of the at least one segment in question, and determining probe-derived attributes from the probe traces for the at least one segment in question, the first segment and the second segment; and determining, by the processor, whether the probe-derived attributes are reliable, and if so, comparing the trend of the probe-derived attributes from the sequence of probe-derived attributes of the first and second segments with the trend of the database attributes from the sequence of database attributes of the first and second segments, and if there is a positive correlation, populating the database attribute of the at least one segment in question using the database attributes of the first and second segments to fill in the missing or verify the unreliable database attribute for the at least one segment in question.