Searching for a Residential Plot in Lexington, MA
Stephanie Galaitsis – UEP 232
In recent years Lexington, MA has been a preferred location for families seeking the
convenience of the city with the amenities of the suburbs. The demand is so great that a trend of “teardowns” emerged, wherein the new family is wealthy enough to purchase land with a house, tear it
down, and build a much bigger house to suit their needs.
The Fiske elementary school district, shown below, is particularly well-suited to these teardowns because when the former pig-farm land was developed in the 1950s, the plot sizes were large
and the houses were modest in size. This project is about the search for a suitable plot for a tear-down.
The family is question wants a large home with space for their children to play, and perhaps a nearby
grocery store. They are concerned with factual accuracies about the neighborhood on the map and the
size of the lot they might purchase. Because they want to build a large home within the town setbacks –
30 feet in front and 15 feet on the sides, lot sizes should be accurate within that range – preferably
within five feet. The other accuracy demands are more connected to information than spatial accuracy.
Legend
Roads - Mass GIS
Roads - Census TIGER
Flow Lines- Census TIGER
Flow Lines - NHD
Water Bodies - Census TIGER
Water Bodies - NHD
Bike Trails
Open Space
Buildings
Tax Parcel
Priv Parcel
Rail Parcel
Water Parcel
")
Schools
Because the roads and water flow lines are from different
sources, their symbology makes it possible to distinguish when
they are in the same place or when data from one source is
alone. Figure 1 shows what overlapping roads and flow line data
sets look like. In the Fiske district, there were no instances
where the flow lines deviated, however the instances where the
roads were different will be discussed in this report.
The pink and black are the Figure 1. Overlapping Vectors
confluence of Mass GIS
and Census TIGER data for
roads, and the chopped
blue is where the National
Hydrologic Dataset (NHD)
and the Census TIGER data
for flow lines overlap.
Similarly, in the image to the right we see the overlap of the NHD water
bodies the Census TIGER water bodies. It appears that the dots from
the legend do not appear well in Word, but the light blue color is NHD
alone, and the dark blue, where unfortunately the dots are also
invisible, is the overlap of the dotted layer underneath the slightly
transparent Census TIGER layer.
Figure 2. Overlapping Shapes
Below is the GIS map of the Fiske School District in Lexington, MA.
Figure 3. Fiske School District, Lexington MA
Roads
It is immediately apparent that there are discrepancies between the Mass GIS roads and the Census
TIGER roads – there seem to be many cul-de-sacs that Mass GIS did not have on record. Furthermore,
there are two situations, such as the one shown in Figures 4 and 5, where an entire road was not
included.
Figure 4. Fiske School District with Inset Map (Missing Mass GIS Road)
This road (pink) was omitted in the Mass GIS data.
Figure 5. Inset Map (Missing Mass GIS Road)
This road, and one of the other
missing roads, is an unpaved
neighborhood road that is not an
official town roads, which may explain
why they were not included in the
Mass GIS data set. However there are
two houses on Ridge Road that are
excellent candidates for a tear-down
because each plot has significant land.
Without the information about the
road, the plots (circled) would not
have seemed feasible for
consideration.
Currency: The roads missing from the Mass GIS data set are old, unpaved roads that neighbors say are
outside of the town’s jurisdiction. Thus the omissions may not be an issue of currency, but of politics.
However, all of the missing cul-de-sacs are developments from the last 15 years, an indication that Mass
GIS road data may be out of date for the Fiske School district. The meta data was unavailable for
confirmation.
Completeness: The Census-TIGER roads include areas that Mass GIS does not. No examples are seen
where Census-TIGER data omits roads that Mass GIS has. Therefore, Census-TIGER is a better choice for
completeness.
Accuracy: The Mass GIS and Census TIGER streets fall within the regions between the property blocks,
and, with some minor exceptions, are predominantly drawn through the centerline of the orthophoto
roads. The family has no reason for dissatisfaction with the complete Census-TIGER road vectors. Figure
6 below shows two minor inaccuracies – one incorrectly locating a very old closed road added by
Census-TIGER, and one with the wrong shape of the road. These are the exception, not the rule.
Figure 6. Miss drawn roads and Fiske Elementary School
The road vectors are so identical that this author suspects that Census-TIGER took the Mass GIS roads
and added more data.
Hydrography
The family wants to know what water recreation activities are available nearby, and immediately a
major inconsistency between data sets is apparent in the northeast corner of the map.
Figure 7. Fiske School District with Inset Map (Water Body Inconsistencies)
The NHD polygons include much more water area than then census TIGER polygons, though they
overlap perfectly on all the water flow vectors. The area with the biggest disreptrancy is shown in the
inset map, examined in Figure 8 with the orthophoto. The NHD data shows a large lake, whereas the
orthophoto shows only marshland without water.
Figure 8. Water Body Inconsistencies
It would seem reasonable to conclude that there is an ephemeral water body that can swell with
precipitation. When the NHD performed their survey, they found water, whereas during the periods of
the orthophoto and the census TIGER data gatherings, there was very little standing water. These
differences affect as to whether there is a large water body for recreation available to the families in the
area.
Additionally, it is observed that the water flow for NHD and Census-TIGER completely overlap, however
they do not distinguish between streams and underground pipes, making it look like the Lower Vine
Brook crosses the road, or flows through front yards. This can create some confusion.
Currency: Currency would not necessarily solve the problem of the swollen lake, because it is a seasonal
occurrence. Other than this disagreement, both data sets have current information.
Completeness: The Census-TIGER and NHD data set may actually show too much water, since some of it
flows underground.
Accuracy: The orthorphotos and personal experience confirm that the placement of the water bodies is
accurate in generalized terms. Water bodies swell and diminish all the time, so a general sense of size
and location is most important.
Bike Paths
The family wants to know whether there are good recreational areas nearby, so a bike trail file was
included in the GIS map. However, it did not reveal any bike paths for the area.
This is an inaccuracy. In reality, a bike path runs the length of Lower Vine Brook, which is surrounded, as
the map shows, by a lengthy nature reserve.
Figure 9. Fiske School District with Inset Map (Missing Bike Path)
Figure 10. Inset Map (Missing Bike Path)
When the bike path is added it, the surrounding
houses become considerably more attractive for
development. In Figure 10, several plots are circled
that have easy access to the bike path and have the
correct combination of small house sizes and large
plot sizes to make a tear-down feasible.
Additionally, no vectors were available to account
for the unpaved nature trails in the area. The bike
trail leads to a wetland area with a lake (shown at
the top of Figure 10) that has trails all around the
northern side, including one that connects it with
the neighborhood directly east of the lake. These
trails have long entertained the children of the
neighborhood and would help with decision making
for future residents.
Currency: The bike path in question has been in
place since at least the 1980s, but the bike path file
meta data says the data was updated in 2002 to
include any trails that permit bicycle travel. The
omission is not issue of currency, but perhaps due
to a threshold definition of what constitutes a bike
path. The Fiske path is a small paved path without
dividing lanes, so perhaps it does not meet the
definition the mappers were using.
Completeness: This record is incomplete.
Accuracy: This record is inaccurate.
Open Space
According to the meta data, the open space polygons in the map represent open public land. People
looking for a beautiful area might believe that their neighbor’s open meadow improves their quality of
life and should be included in the GIS map. Figure 11 shows the inset map where open space has not
been labeled.
Figure 11. Fiske School District with Inset Map (Missing Open Space)
There is a large open space in this inset without any buildings, and when it is cross-referenced with the
orthophoto, it is revealed to be a large meadow.
Figure 12. Inset Maps (Missing Open Space)
This open space was not
included in the open space
polygon.
An additional mapping
inaccuracy is evident in the
upper left of the inset map –
the Open Area vector extends
out into the street, suggesting
that while its general place is
correct, the borders may be
off by several feet.
Currency: Were the issue currency, there would be too much open space because the Fiske school
district has been undergoing rapid development. The meta data for the file clarifies that the omission is
due to political definitions of open space, which cannot be privately owned, as above meadow is.
Completeness: There is much more open space in the Fiske School district than is included in the open
space polygons, and this information will matter to families looking to move there.
Accuracy: The open space polygons are not precisely drawn, extending multiple feet beyond their
borders. However, for the purpose of property shoppers, exact accuracy of open space – which is
already relatively amorphous – is not as important as knowing where the areas of open space are to get
a sense of what the neighborhood looks like.
NAICS Georeferencing: Grocery Stores
There are no grocery stores in the Fiske neighborhood according to NAICS data. This is accurate. For
many years there was a farm stand in the middle of the neighborhood, but it closed several years ago
and thus is no longer included in current data available for GIS mapping.
Currency: The data is current.
Completeness: The data is complete because there are no longer any grocery stores in the area.
Accuracy: The data is accurate.
Schools
Fiske elementary school is included on the map, and the data layer places it directly on top of the
building footprint, which is verified in the orthophoto. The label, however, is “Fiske” – seen in Figure 6 –
and unlike nearby “Wm Diamond Middle”, it does not give a suggestion as to what type of school it is.
Currency: The data is current.
Completeness: The label is incomplete, ambiguous, and inconsistent with nearby labels.
Accuracy: The data, besides the name, is accurate.
Building Footprints
Property lines and building footprints are extremely important for the purposes of a family seeking to
move to the Fiske school district, and while some problems arise, the data seems largely dependable for
the family’s purposes.
Inaccuracies were discovered in regards to current building projects, both having to do with the timing
of the GIS data sets. In Figures 13 and 14, the orthophoto and the building footprint do not agree.
Figure 13. Missing House
The building footprint (2011-2012 data) is more recent than the orthophoto (2008 data), evidence that
this building has already been torn down, most likely for a larger house like its nearby enormous
neighbors that are also recent tear-downs.
Figure 14. Wrong Buildings
The green houses shown in the orthophoto
were torn down to make way for the housing
development whose footprint is shown in the
more recent building footprints polygons.
More units are currently under construction.
Currency: The building footprints show
current development – but because houses
are being torn down and rebuilt all the time,
building footprint currency will be a challenge
for the future planning in the Fiske school
district.
Completeness: Using the orthophoto, there appears to be excellent coverage of the building footprints
in places where there are any types of structures.
Accuracy: With the orthophoto it can be seen that building footprints are extremely accurate. There are
some circumstances where the polygons may have be shifted a foot or so, but for the family’s purposes,
the footprint file is extremely helpful to give an idea of what houses are good candidates for a teardown.
Property Lines
Property lines are difficult to judge because they are not tangible features on the land. In fact, surveyors
and maps define them, rather than the other way around. However, using the orthophoto, it can be
seen that the property lines often coincide with midpoints between houses or areas where dense
vegetation grows, suggestion that the current residents’ idea of property boundaries matches well with
the legal definitions.
Figure 15. Property Lines
Currency: There are examples of changes in property lines, known to the author, that are reflected or
not reflected on the current map. The data is from 2011-2012.
Completeness: There is no reason to believe the data is incomplete.
Accuracy: With the orthophoto, the data appears to be accurate, but only as much as legal boundaries
can be manifested in actual boundaries.
Conclusion
Many data inaccuracies arise between various data sets, due to the rapid development of the Fiske
neighborhood, even within the span of five years.
Census TIGER roads, water bodies and water vectors have all proven extremely accurate when
compared with the orthophoto and with on-site experience. However, the orthophoto is from 2008, so
while it is excellent for confirming features with minimal change – water bodies, schools, open space,
property lines – it is outdated when it comes to development. For the purposes of choosing a lot, the
most recent data must be used, and that would be the 2013 building footprints from Mass GIS, although
even those appear to be from before 2012 because the newest developments over the green houses are
not included.
The most inaccurate polygons appear to be the bike path and the open space, which is not clearly open
public space until the meta data is reviewed. Unlike the detailed building footprints, the open space
borders borders are generalized and it purposefully excludes open areas on private property. This, along
with the omission of the bike path, can greatly influence how the family perceives the Fiske school
district.
In short, it appears that the Census-TIGER data for roads and water features and the recent building
footprint data should be used in conjunction with the school, property lines and open space data for
estimating where to build the next big house.