The Time Dimension - Introducing Geographic Information Systems with ArcGIS - page 571

representing the road segments that were coincident. Those that weren't coincident are not
shown. Check the drop-down menu in the Preview text box at the bottom of the display. You will
notice that there is no table associated with the topology.
13. Launch ArcMap with a Blank Map. Dismiss the ArcCatalog program but bring up the Catalog
sidebar (Windows > Catalog) in ArcMap. Drag Lex_Roads_2002 and Lex_Roads_1994 from
IGIS-Arc_ YourInitials \Historical_Data\Roads.mdb\Lexington_SP_North_83_Feet
onto the map.
14. In the T/C make the 1994 roads black, width 1. Make the 2002 roads bright green, width 1.
Arrange it so that the 1994 roads are drawn last—that is, place its entry at the top of the T/C.
You can see that most development occurred along the southern and eastern edges of the city.
Running “topology” on the data sets has snapped some features of the data sets together,
where appropriate. Add the
Lexington_SP_North_83_Feet_Topology
to the map. (Don't add the associated feature classes—they are already there.) Now individual
road segments can be identified, so the new ones can be picked out. Generally, whatever is
green is new. Not so good is this: If you zoom in on some areas, you will notice that roads
that are probably meant to be the same still show up in both data sets. For example, Label
Features for both Lex_Roads layers. Then use Selection > Select By Attributes. For Layer pick
Lex_Roads_2002. Noting the single quotation marks, put in the query
[FENAME] = 'Elmendorf'
Click Apply. Click OK. Now use Selection > Zoom to Selected Features. Clear all selections.
What you will see is two segments of Elmendorf that go their separate ways for a bit and then
re-converge. The topology operation did not see them as almost coincident, although all the
other roads around them were flagged, in pink, as errors.
Frankly, older TIGER/Line data left a lot to be desired, so there are segments such that at least
one vertex in a feature was more than 50 feet away from vertices in the same feature in the
other data set.
15. Let's further improve the presentation. It would be nice if we could use the topology data set to
erase the 2002 roads that are coincident with the 1994 roads. Bring the Topology toolbar and
the Editor toolbar into view. In the Table of Contents, make sure Lex_Roads_2002 is on, as well
as the topology. Turn off Lex_Roads_1994.
16. Choose Selection. Select By Attributes. Select those roads in Lex_Roads_2002 with
FENAME equal to 'Strawberry', putting Strawberry in single quotation marks. Zoom to the
selection and then clear selected features. Using Layer Properties, make sure the features
in Lex_Roads_2002 are labeled with FENAME. Using Placement Properties, in the Duplicate
Labels section, select Place one label per feature part. OK. Apply. OK. Note that portions
of Strawberry in Lex_Roads_2002 are flagged, by the pink of the topology, as overlapping
Lex_Roads_1994.