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.
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'.
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.
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.
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)".