Examples of Edge Matching Problems and Solutions by iht11609

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									  Examples of Edge
Matching Problems and
      Solutions
                  First, a brief definition of “edge
                              matching”

“Edge matching” is defined by the University of Minnesota’s online
GIS glossary as follows:

      The comparison and graphic adjustment of features that cross
      adjoining map sheets to ensure that the features intersect the
      boundary at a common, coincident location. A "seamless"
      database is thereby created.
       (http://www.extension.umn.edu/distribution/naturalresources/components/DD6097ag.html)




It specifies the goal of “seamless” data and defines very generally
the processes of comparing and adjusting the data to reach that
goal.
                 “Edge matching” road data
                  for addressing and 9-1-1


We’ll be discussing edge matching only as it relates to road
centerline GIS data used for addressing and 9-1-1 call location.
There are 3 elements of road data that must be edge matched:

        1. The lines representing the roads themselves,
        2. The names of the roads on each side of the boundary
           and
        3. The address numbers/ranges on each side of the
           boundary.

Of course, road names and address numbers often change at
political boundaries and can even be different on each side of the
same road.
                 “Edge matching” road data
                  for addressing and 9-1-1
Most of the edge matching process involves comparison of each
road that crosses or follows a boundary to determine whether
adjustments will be needed and, if so, specifically what
adjustments are needed.

It generally makes the most sense for local agencies to meet with
their neighbors and make corrections themselves after careful
examination, collaboration and mutual agreement. This requires
several things that may be in short supply depending on those
involved:
        1. Cooperation,
        2. Time,
        3. Understanding of GIS and addressing,
        4. Authority to make edits to addressing and telco
            databases as needed and
        5. Planning for ongoing edge matching as needed.
                  “Edge matching” road data
                   for addressing and 9-1-1




With the advent of NG9-1-1, there will be a need for edge matched
data across the state far sooner than appears to be possible by
organizing separate meetings between most GIS/addressing
agencies around the state.

Centralizing this work has several benefits and may, in fact, result
in more local interest in undertaking the work.
               Edge Matching Problems and
                       Solutions



The following slides will illustrate edge matching problems and
combinations of problems that are currently known to exist in the
NM 9-1-1 GIS Database.

For each problem, a solution has also been identified and
illustrated. It is worth noting that there are generally many ways
to eliminate an edge matching problem. The more time and
information at the disposal of the GIS Analyst, the better job they
will be able to do in reaching appropriate solutions.
Edge Matching Problems and
        Solutions:
         SNAPPING
        PROBLEM:

        A “snapping” problem occurs when two
        roads that connect to each other on
        the ground do not do so in the GIS
        data.

        Two visible instances are shown with
        red circles to the left but please note
        that these types of problems can be
        too small to be seen and can
        sometimes only be identified by GIS
        tools.

        The danger of having roads unsnapped
        is that software will not recognize
        them as being connected.
Edge Matching Problems and
        Solutions:
         SNAPPING
        SOLUTION:

        This is perhaps the easiest sort of
        problem to correct in that the GIS
        Analyst does not generally need to
        spend as long determining the best
        solution.

        They can simply correct the problem
        using standard GIS tools so that the
        exact location of the start of one
        segment is identical to other segments
        it is supposed to connect to. In this
        case, the corrections were made so
        that the roads connect to their
        neighboring features right at the
        county line.
Edge Matching Problems and
        Solutions:
DUPLICATE ADDRESSING AT BORDERS
          PROBLEM:

          Although the GIS Analyst has made
          the necessary corrections to the
          snapping problems, there is also a
          problem with the address range
          attribution for Hobbs Hwy at the
          county line.

          On the next slide, both are
          highlighted in blue. The Lea version of
          the highway has the value “LE_CO” to
          the left side of the table. The Eddy
          version is marked with “ED_CO”.
                                 (continued…)
                 Edge Matching Problems and
                         Solutions:
                DUPLICATE ADDRESSING AT BORDERS


(PROBLEM …continued)

Notice how the Eddy County version ends at 6242 in possible
addressing while the Lea version starts at 6200. Since both have the
exact same name and are in the Carlsbad community, that means that
any address from 6200 to 6242 could “map” to either side of the
county line.
                Edge Matching Problems and
                        Solutions:
               DUPLICATE ADDRESSING AT BORDERS
SOLUTION:

The GIS Analyst examined the length of the roads and total number of
addresses available (6169 through 6281, roughly 112 addresses). They
determined that the Eddy feature accounted for 72% of the length of
the two combined and, therefore, assigned 72% of the available
addresses to that feature (80 addresses). They edited the “high”
values of the Eddy feature accordingly then edited the “low” values of
the Lea feature so that it picks up where the Eddy feature’s address
range left off. The red circles show the changed values.
Edge Matching Problems and
        Solutions:
      FEATURE OVERLAP

        PROBLEM:

        Data Sources often submit road
        features that completely or partially
        overlap features in the neighboring
        data.

        In this case, De Baca County has
        submitted portions of Urton Lake Rd
        and Salt Lake Rd within Chaves County.

        (Note also that the 2 Data Sources
        disagree about which road is Urton
        Lake Rd.)
Edge Matching Problems and
        Solutions:
      FEATURE OVERLAP
        SOLUTION:

        The GIS Analyst removed the
        overlapping De Baca County features
        (as they were in Chaves County) and
        then snapped the features together at
        the county line (see the red circles).

        They also investigated the road name
        disparity using publicly-available data
        (GoogleEarth in this case) and found
        that the Chaves County data had the
        names switched for Sea Rd and Urton
        Lake Rd. After first checking the
        address ranges appropriately, they
        switched the names.
Edge Matching Problems and
        Solutions:
FEATURE SPLITTING and ADDRESS
  RANGING ON BORDER ROADS
         PROBLEM:

         This is a classic example of the sorts
         of problems found along county line
         roads. In this case, Otero County and
         Dona Ana County each have slightly
         different versions of the road and
         each is responsible for its own side of
         that road.

         It is a standard GIS rule to always
         start a new feature at each
         intersection with another feature and
         Dona Ana County has done that along
         County Line Rd, splitting it at Rocky
         Mountain Rd. (See the red circle.)
                                (continued…)
Edge Matching Problems and
        Solutions:
FEATURE SPLITTING and ADDRESS
  RANGING ON BORDER ROADS
         (PROBLEM …continued)

         The table below shows original
         attribution of the 2 Dona Ana
         features. Notice how they have
         included address range data for both
         sides of the road despite only being
         responsible for the west/left side. It
         would have been more appropriate
         here to put zero values in for the
         right-side address range – the typical
         convention for this situation.




                               (continued…)
Edge Matching Problems and
        Solutions:
FEATURE SPLITTING and ADDRESS
  RANGING ON BORDER ROADS
         (PROBLEM …continued)

         Otero County has not taken into
         account the existence of Rocky
         Mountain Rd on the other side of the
         county line and has therefore not split
         their version of County Line Rd at that
         intersection. (One road feature
         extends from Lisa Dr to Old Laredo
         Rd.) They have “zeroed out” the left
         side address range, however.




                                (continued…)
Edge Matching Problems and
        Solutions:
FEATURE SPLITTING and ADDRESS
  RANGING ON BORDER ROADS
         (PROBLEM …continued)

         Of course, this picture also shows a
         disparity in the location of the road
         but it is relatively small – see the gap
         between the two versions of County
         Line Rd (shown in white).

         It is also interesting that the two
         sources don’t agree on the extent of
         this road as Dona Ana has it going
         further north than Otero and Otero
         has it going further south.
                 Edge Matching Problems and
                         Solutions:
                  FEATURE SPLITTING and ADDRESS
                    RANGING ON BORDER ROADS
SOLUTION:

Before splitting the Otero feature at the intersection with Rocky
Mountain Rd, the GIS Analyst first made spatial edits to make it match
the Dona Ana version of the road perfectly (and “snap” to both
datasets). The Dona Ana data lined up better with aerial photos of the
area.

The Analyst did not attempt to move both features to follow the
county line as shown because they were aware that the road data more
accurately depicts the county line.

It is appropriate in this case for each Data Source to have a feature in
their data that represents one side of the road as they are each
responsible for their own side.
                                                      (continued…)
Edge Matching Problems and
        Solutions:
FEATURE SPLITTING and ADDRESS
  RANGING ON BORDER ROADS
         (SOLUTION …continued)

         The GIS Analyst split the edited
         Otero version of the road into two at
         Rocky Mountain Rd and the result is
         that the Otero and Dona Ana versions
         of those 2 blocks (shown in light blue)
         are stacked on each other so neatly
         that you cannot see that there are 2
         features there. They also split the
         original Otero address range (600-
         650) in half as shown below:

								
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