Merging data enables
you to construct maps that show larger geographic areas without the
overhead of storing duplicate spatial data sets. For example, you
might have chains, nodes, and details data sets for each U.S. state.
If you want to create a map of New England, you do not have to physically
combine and duplicate the individual data sets for the six states
composing the region. Instead, you can create a merged spatial entry
named
New_England
that references the
individual states' simple spatial entries.
Edge matching provides a mechanism to update adjoining
spatial data sets to replace missing left or right values in the chains
data sets. Let us use the New England example. There are chains in
the chains data set for New Hampshire that lie along the Vermont border.
These chains contain the FIPS code of 33 on one side of each chain.
The other side of each chain has a missing value. The corresponding
chains in the Vermont chains data set contain the Vermont FIPS code
of 50 on one side and a missing value on the other side. An edge match
merge of the two data sets locates these common boundary chains in
each data set. It replaces the missing values with the correct FIPS
code for the adjoining state. It will also create a merged spatial
entry that references the New Hampshire and Vermont simple spatial
entries.
The EDGEMATCH operation
creates a single merged spatial entry by which you can create a map
of the two states. It also adds the Vermont FIPS code to the appropriate
chains in the New Hampshire data set. In addition, it adds the New
Hampshire FIPS code to the corresponding chains in the Vermont data
set.