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  • Etingoff- Assignment 6

Kim Etingoff

GIS Assignment #6

4/14/14

 

Project Description

 

For the final project, I will be conducting a site suitability analysis of parcels in Somerville. The analysis will be focused on identifying parcels that are appropriate for being developed as green space in Somerville, based on a variety of factors. One underlying assumption involved is that Somerville is in need of more green space, defined in this project as open public spaces covered in vegetation. The Land Use Technical Report [1] released by the City of Somerville’s Office of Strategic Planning and Community Development determined that the percentage of land dedicated to green space in Somerville is lagging behind that of neighboring communities. The City is furthermore dedicated to increasing the amount of green space available to the public, as detailed in the Somerville Open Space and Recreation Plan 2008–2013 . [2] The City, along with many others, recognizes that green space provides a host of benefits, touching on physical and mental health, environmental service provision, community cohesion, and more.

 

Two main factors will be involved in the suitability analysis. First is the issue of equity of access to green space. A variety of data will be analyzed to determine areas within Somerville that are in need of more green space, since green space is not equitably distributed within the city, nor do all residents have equal access to existing green space within and outside of the community. Second is parcel appropriateness. Somerville is a densely settled city with limited undeveloped areas. Still, green space may be introduced to certain parcels that are either already developed or are vacant. Commercial rooftops and land held by private interests have the potential of being converted to public green space, as they have been in Seattle and San Francisco. [3] [4] Vacant lots represent other potential green space sites. This project will seek to identify parcels that are both structurally appropriate and that address issues of access equity within Somerville.

 

 

 

 

 

 

 

Spatial Questions

 

This project will try to answer the following questions using GIS technology.

 

  1. Are there currently areas in Somerville that lack access to green space in the immediate vicinity, as compared to other areas?
  2. Are there currently areas in Somerville that lack access to green space outside of the immediate vicinity, compared to other areas?
  3. Where should new green space be placed to create more equal access to green space within the City of Somerville’s boundaries?
  4. Which already-developed parcels in Somerville can be converted at least partially to green space use?
  5. Which undeveloped parcels in Somerville can be converted into green space?

 

 

 

Literature

 

Byrne, Jason and Neil Sipe (2010). Green and open space planning for urban consolidation—A review of the literature and best practice. Brisbane, QLD: Griffith University.

 

This literature review offers a good conceptual background in green space planning. Specifically, it points out that city residents do not all have the same green space needs, and that the best green spaces are multi-use and are attractive to a variety of people. Thus, the quality of green space (and open space without vegetation) is important, not just the quantity. The authors review many of the benefits access to green space confers on communities, from mental health, to decreasing obesity, to revenue creation. The study also provides a comparison of park spatial standards. In the United States, the most recent standards, which are admittedly old, stipulate that each 10 acres of park should serve 1,000 residents, and should be located within ¼ mile of them. These standards don’t take park quality into account and have not always been achieved (such as in Somerville). The review also covers GIS methodology, and suggests including green space distribution data, accessibility data, and demographic data to determine equity of current and future green space development.

 

 

Comber Alexis, Chris Brunsdon, and Edmund Green (2008). “Using a GIS-based network analysis to determine urban greenspace accessibility for different ethnic and religious groups.” Landscape and Urban Planning 86 : 103–114.

 

This article uses network analysis to answer questions about how access to green space is related to demographics. The authors explore not just the amount of green space in Leicester, England, but examine its distribution in relation to different ethnic and religious groups. They used network analysis to determine the distances between green spaces and the centers of census groups of about 300 people each. The paper further asks which areas in the city need to have enhanced green space provision based on findings of inequitable access and published green space guidelines that suggest parameters for public access to green space (i.e. people should live within 300 meters of green space, etc.). Many of these ideas and methodology can be applied to a Somerville context.

 

 

Stahle, Alexander (2010). More green space in a dense city. Urban Design International 15, 47 ­ –67.

 

This study is useful for thinking about the relationship between a green space’s accessibility and attraction, defined traditionally as distance and surface area. The paper proposes new ways of understanding accessibility and attraction. The latter is especially relevant to this project, since it redefines attraction as use value. GIS can incorporate the number of use values of a green space into analysis, to provide a better picture of the importance of any one space. The authors created a “sociotope” map as part of their research, depicting several use values of green space. They found that combining use values, green space area, and distance to green space was correlated with how people perceived their own access to green space. 

 

Uy, Pham Duc and Nobukazu Nakagoshi (2008). Application of land suitability analysis and landscape ecology to urban greenspace planning in Hanoi, Vietnam. Urban Forestry & Urban Greening 7 , 25 ­ –40.

 

The authors offer an example of land suitability analysis as applied to urban green space in Vietnam. They detail the criteria used for land suitability, and the method for applying criteria using GIS, including weighted scoring, which is appropriate for this project. The study also goes further and assesses the overall amount of city green space, recommending that the city increase land dedicated to green space and proposing spaces that can be used for this purpose. Similar conclusions may be made for Somerville after a land suitability analysis.

 

 

Wolch, Jennifer, John P. Wilson, and Jed Fehrenbach. Parks and Park Funding in Los Angeles: An Equity-Mapping Analysis. Urban Geography 26(1), 4–35.

 

This paper lays out a park equity mapping analysis. The authors point out that there are two sources of unequal access to green space—actual unequal distribution, and socioeconomic factors that lead to uneven ability to use the space available (such as being able to afford a membership at a pool, ability to drive to a larger park, etc.). For the analysis, they define access as living within a quarter mile of a park edge. Quarter mile park buffers were created to determine access. The researchers determined park acres per 1,000 population, percent of census tract population living within the buffer zone, and park acres per 1,000 population in the buffer zone. They found, among other things, that lower-income households had inferior access to parks.

 

 

Data Layers

 

Name

Description

Source

Attributes

Somerville parcels

2009 (most up-to-date parcel data does not have needed attributes)

City of Somerville on Tufts GIS data server

Zone, use code,

acres (needs to be calculated)

Protected and recreational open Space

More comprehensive green space identification than Somerville open space data; 2014

Mass GIS

Public access, primary purpose, acreage, interest codes

Bike trails*

2004

Mass GIS

Trail status

Building structures (roofprints)

Outlines of buildings; 2014

Mass GIS

Acres (needs to be calculated)

Poverty by census tract

poverty information joined to census tracts

American Census Survey 5-year estimate, 2010; American Census Bureau Tiger data

Number of people that have experienced poverty in the last year (per census tract), number of total people (per census tract)

MBTA nodes

Used to identify T stations at least partially in Somerville; 2006

Mass GIS

none

EOT Roads

Part of basemap; roads maintained by MassDot; 2012

Mass GIS

class

City boundary

Part of basemap; 2005

City of Somerville on Tufts GIS data server

none

Hydro

Part of basemap; 2010

Tufts GIS data server

none

* On closer inspection, although this bike trail dataset is from 2004 (and I’ve been unable to find anywhere with updated data), it is almost entirely accurate for Somerville, with the exception of one line. If there is a way to change that single line data, I could update the dataset for this project. Otherwise, I will contact the city of Somerville.

Preparation and Analysis Steps

 

  1. Import all data layers and project into appropriate coordinate system ( 1983 State Plane Massachusetts Mainland FIPS, feet).

 

  1. Create base map of Somerville.

 

  1. Join census tract data and poverty data, using tabular Join and Relate tool.

 

  1. Calculate all areas (acreage) needed for data sets.

 

  1. Join open space data layer to bike trail data layer
    1. Select by attribute for existing and planned bike trails in Somerville.
    2. Use spatial Join and Relate tool to join this selection with open space data layer and create a more inclusive open space layer.

 

  1. Proximity analysis for open space
    1. Select by attribute for all polygons in open space data layer that are publically accessible and create new data layer.
    2. Use the raster Euclidean Distance tool to create a raster grid showing distance away from open space.
    3. Reclassify proximity to green space:

1-     under 1/16 mile

2-     1/16-1/8 mile

3-     1/8-1/4 mile

4-     more than ¼ mile

 

Note: I would like to somehow combine proximity to any green space with the proximity to green space that is both larger and with multiple uses, perhaps using the primary purpose attribute in the open space data set or joining the open space data to parcel data and using the use code attribute under parcels. I don’t strictly have to perform whatever steps that may entail in the interest of time, but it would make this project more in line with what I’m envisioning and the results more interesting. 

 

  1. Proximity analysis for MBTA nodes
    1. Use the raster Euclidean Distance tool to create a raster grid showing distance away from T stations
    2. Reclassify proximity to T station

1-     under 1/16 mile

2-     1/16-1/4 mile

3-     1/4- 1/2 mile

4-     1/2-1 mile

5-     more than 1 mile

 

  1. Poverty by census tract data
    1. Convert poverty by census tract data to raster form using the Polygon to Raster tool.
    2. Reclassify poverty by census tract (1 is highest income, 5 is lowest income).

 

  1. Use the Raster Calculator tool to combine all reclassified data sets and change color ramp for clarification. Proximity to open space will be weighted the most, followed by poverty, and proximity to MBTA nodes.

 

  1.                      Vacant lots
    1. Use Select by Attribute tool to identify all parcels with an assessed parcel value of zero and create new data layer.

 

Note: Can I assume an assessed parcel value of zero means a vacant lot? The metadata lists several use codes that could be helpful for identifying vacant parcels, but the dataset does not include any parcels with those use codes, even though I know there are at least a handful of vacant lots in Somerville.

 

  1.                      Rooftop parcel suitability
    1. Use Spatial Join tool to join building structures and parcel selections, in order to assign zoning codes to building structures.

 

Note: Spatial Joins will not work well to join polygons to polygons. Should I convert structures or parcels to points first before joining, or is there a better alternative for doing the steps below?

 

  1. Use Select by Attribute tool to identify building structures located in commercial or institutional zoning districts.
  2. Use Select by Attribute tool again to identify buildings with rooftop footprints over 1/8 acre and create new data layer.

 

  1.                      Commercial building land
    1. Use Erase tool to get rid of building structures from parcels.
    2. Use Select by Attribute tool to identify commercial and institutional parcels.
    3. Use Select by Attribute tool again to identify parcels that are still at least 1/8 acre and create new data layer.

 

  1.                      Overlay combined raster data set with the site choices found through the vacant lot, commercial rooftop parcel, and commercial land analyses.
    1. Convert raster data set to polygon using Raster to Polygon conversion tool.

 

Note: This seems clunky to convert data sets to rasters and then back to polygons. Is there any way to streamline this?

 

  1. Overlay new polygon data set with the vacant lot, commercial rooftop parcel, and commercial land data sets with the Intersect tool.
  2. Create final data set of parcels that fit all criteria.

 

 

Poster

 

The final poster for this project will include information on project background as well as data sets used, methodology, and goals/research questions. The maps that will feature on the poster will likely be:

 

  3 small maps showing the original raster data (distance to open space, T stations, and poverty)

  a medium-sized map showing the combined raster data sets that depict site suitability oriented toward equity

• the   largest map will show the combined equity dataset with the parcel suitability layers (vacant land, rooftops, and commercial land)

 

Each map or set of maps will have text explaining their purpose and why the criteria were chosen, as well as how they’re relevant to answering the posed questions.

 

 

 

 

 

 

 


[1] Office of Strategic Planning and Community Development (2011). Trends in Somerville: Land Use Technical Report. http://www.somervillema.gov/sites/default/files /LandUseTrendsReportFinalMay2011.pdf.

[2] City of Somerville (2009). Somerville Open Space and Recreation Plan 2008–2013 . http://www.somervillema.gov/sites/default/files/documents/2008-2013-OSRP-NarrativeAndAppendicesFINAL.pdf.

[3] “Privately-Owned Public Open Space and Public Art.” San Francisco Planning Department. Last updated October 6, 2013. http://www.sf-planning.org/index.aspx?page=3339

[4] “Privately Owned Public Open Spaces.” Settle City Council. Accessed April 13, 2014. http://www.seattle.gov/council/licata/public_space.htm