A three step procedure was used to prepare the
analysis for the critical root zone project. I obtained rectified-orthophotos.
The next step required digitizing impervious areas including rooftops,
sidewalks, and driveways. The last step was buffering the impervious
areas based on realistic DBH
as defined by the City of Ann Arbor.
Orthophotos:
I obtained the rectified-orthophotos from Mr.
Merle Johnson, Information Services Division. The City of Ann Arbor
in 1992 (early 1993) sent a RFP (request for proposal) and RFQ (request
for qualification) to approximately 250 potential clients. Fifteen
clients responded to the RFP; whereas, six firms were selected for further
consideration. Those six firms were solicited for additional detail
including the ability to generate a geodetic framework and terrain modeling.
From those six firms, three firms were selected based on technical merits
for a more thorough evaluation. The final candidate selected was
Woolpert, LLB of Dalton, Ohio. Woolpert, LLB was selected because
they performed all the functions necessary to create orthophotos.
The work was completed in 1993-1994. In 1997, an update was completed
for selective areas and a complete fly-over of the city. The image
is a 1' resolution digital orthophoto measuring 30" x 30" at a scale of
1" = 125'.
Feature Types:
The subject area chosen for this project was
the Bromley Subdivision, located in northern Ann Arbor. The image
is a rectified-orthophoto . Three feature types were identified to
be digitized due to their impervious area. All rooftops, public sidewalks,
and driveways were digitized.
Methodology:
Digitization:
I used ArcView 3.2 as the application to perform
the digitizing. The initial step began by creating a new theme.
From the "view" menu, select a "new theme". I zoomed over the targeted
area between 1:200 - 1:300 scale. Make the "new theme" active; select
"start editing" under "theme". Select "create a polygon" tool to
create each polygon. Caution: perform 'save" data often.
Buffering:
Use "create buffers" under "theme" menu.
For the next step use "the features of theme" for "what do you want to
buffer"? Select "next". I specified my predetermined distance
in feet. I buffered each feature type with a 2-foot zone, 5-foot
zone, and a 10-foot zone. Additionally, I performed a 20-foot zone
buffer for rooftops. The next step use "dissolve barriers between
buffers". For "create buffers so they are" option - I chose "only
outside the ploygon(s)".