Allie Quady
Assignment 5
March 4, 2008
Project Outline:
This hypothetical project will assess potential for wastewater reuse in the Charles
River Watershed. Based on water use needs of the watershed and water availability, the
project will ascertain the amount of potential wastewater reuse. To aid in project
development, an assessment of data quality for underlying geographic and demographic
spatial features was undertaken. In the following pages, information about the data
accuracy of roads, rivers and land use characteristics is examined. The location of
MWRA water pipes in comparison with the location of water according to hydrography
data layers is assessed. The accuracy of information and locations regarding public water
supplies is examined in comparison to orthophotos and to the land use data layer. Land
cover raster data is compared with land use vector data for accuracy and ease of use with
regard to future project needs. Each map shows an area of the Charles River watershed in
order to compare the data quality from each source.
Examination of the data has shown that larger scale Mass GIS roads and rivers,
(1:25,000 ft) as well as a combination of vector and raster data will best serve the
purposes of background layers for the mapping project.
This project will require several more data layers than the base layers that are
represented here. An important layer that has not yet been identified will be locations of
wastewater treatment plants and their monthly return flows, wastewater conveyance and
the populations served. Another necessary layer is water usage within the Charles River
Watershed. To retrieve these layers, the agencies responsible for water use and reuse will
be contacted.
Hydrologic Data:
Map 1: Orthophoto of ponds in Charles River Watershed shows greater accuracy with
Hydro 1:25,000 clip (light grey) than with Hydro 1:100,000 clip (yellow), both from
Mass GIS. Census 2000 rivers (red) show the least accuracy in comparison with the
aforementioned layers in the orthophoto. Positional accuracy of the Census 2000 rivers
was measured to be between 490 ft. and 0 ft. of the orthophoto stream banks. Postional
accuracy of the Mass GIS 1:100,000 was measured at 50 ft and at 0 ft of the stream bank.
Positional accuracy of the Mass GIS 1:25,000 clip was between 3ft and 0ft of the stream
bank.
Map 1
Map 2 involves three hydrologic layers using polygon data. The three layers, Hydro
1:25,000 (light grey) and Hydro 1:100,000 from Mass GIS (dark blue), and Census 2000
Hydro Poly (grey) from the same source as the Tiger roads, show differing levels of
detail. As to be expected the large scale Mass GIS 1:25,000 Hydro poly layer shows the
greatest detail, with a positional accuracy between 0-3ft. The Hydro 1: 100, 000 Poly
layer is accurate between 0-50 ft. The census layer is accurate between 0-490 ft.
Map 2:
Map 3 shows The Mass GIS 1:25,000 Arc Hydrology layer (blue), the Census Hydrology
layer (red) and MWRA water transmission pipes (white). This provides an example of the
Mass GIS data layer following the pipes, whereas the Census data do not include this in
their hydrology data set.
Map 3
Road Data:
Map 4: Orthophoto of roads section: Mass GIS roads are shown in purple, Street Map
Roads are shown in red, and Census 2000 roads are shown in Green. Roads from Mass
GIS show greater accuracy in reference to the orthophoto. The Census roads are the
bottom layer, and when they intersect with street map roads, the layers turn yellow.
Census and Street Map roads vary in accuracy to orthophoto road centerlines by as much
as 95 feet and as little as 7 ft. Mass GIS roads vary by as much as 3 ft and as little as 0 ft
from orthophoto road centerlines.
Map 4: Land Use Overlay: The land use corresponds well to the orthophoto in most
cases. In this picture there is one clear mistake, wherein an industrial area is inaccurately
placed slightly above the actual area in the orthophoto, see red arrow. Positional accuracy
is difficult to assess because in many cases, it is difficult to tell from the orthophoto
where exactly the land use changes.
Map 4: Land Use Overlay
Legend: Pink = forest; Grey = industrial; Light purple = transportation; Blue = water;
Light pink = commercial; Residential = green.
Map 5. Orthophoto for comparison with Map 4, shows the actual industrial zone, without
the land use overlay.
Map 6 below represents a zoomed in picture of further inaccuracies in the land use data
set. The pink areas represent forest and the green areas represent residential areas. The
layers are offset by approximately 150 feet from where the orthophoto shows the forest
and residential areas to actually reside. Map 6:
Map 7: Position of Public Water Supplies: The dot below marks the location of a public
water supply reservoir and is accurately placed directly above what looks like a pump
house (within a foot of directly above) next to the reservoir. On further inspection of the
identifying attributes, the Public Water Supply is identified as the Stony Brook Reservoir,
in the town of Cambridge. The reservoir is actually located in Weston. Of the seven
public water supplies in this area, all except one were correctly identified. This data set
will be useful for quickly locating wells, reservoirs, and other water supplies.
Map 7
Map 8: Impervious cover from the National Land Cover Data Set represents raster data.
Black represents impervious cover. Notice the white line that follows the river: pervious
land cover. Black areas are the most developed areas, covered with asphalt, pavement,
and buildings. This will be an important data source to assess run-off, which might be
applicable to water reuse capacity in the area.
Map 8
Map 9: Land Cover from the National Land Cover Data Set is a second of example of
raster data. In comparison with Maps 4 and 6 representing polygon land use data, raster
data provides gradations within each land use area. Raster images will be useful when
investigating physical changes to the landscape over time, because it is collected more
frequently than satellite imagery. For continuous data, such as water use over time, the
raster data model will be helpful.
Map 9
Legend: Dark blue = water; Blue = Emergent herbaceous wetland; Light blue = woody
wetlands; Dark red – very light pink: gradation from high intensity development to low
intensity development, with the lightest color representing developed open space; Light
green = deciduous forest; Dark green = evergreen forest; Yellow = pasture.
Map 10 shows the raster land cover data set overlaid by the vector land use data set. Note
that the land cover data set gives gradations of color (representing changes in land cover)
within the polygons of the land use data set, which would otherwise be represented by
solid colors depending on land use.
Map 10.