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Designing for Visibility with GIS

For people with sight, the landscape can be considered and remembered as a series of views; a network of prospects. If this is true, then design of the built environment, decisions of where to build or to demolish or to leave areas alone, might consider the effects upon views and visibility. This page demonstrates several capabilities, issues and options for modeling visibility in GIS. This demonstration was carried out using ArcGIS Version 8.3.

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Lets suppose that the owners of a large cranberry processing factory are interestrd in enhancing the image of their factory grounds. As part of an overall landscape enhancement, a historic plaque is to be placed along the road above the plant, where motorists can stop and read about the history of the cranberry factory while looking down on the historic site. How can GIS help to evaluate and design this overlook?

First, we will consider the raw data for representing the site.

Georeferenced Airphoto: Showing the site and the road.

Digital Elevation Model: represents the lay of the land.

Synthetic Hillshade: provides a more evocative representation of landform.

Shaded Elevation Map: Elevation with hillshading provides a base for selecting a site for the overlook.

Viewpoint: A shapefile is created to represent the x aand y location of the overlook on the road above the plant.

WIth these data resources, a GIS -- in this case, ArcGIS, can calculate the intervisibility between each cell in the elevation model and our observer station. Options are available for setting the height of the observer, and the height of the objects being looked at. These options create a fairly relaistic model of visibility, unless we want to consider the interference of vegetation.

Simple Visibility

Offset of Eye-Height

Offset of Objective

Interference of Vegetation

If we want to be realistic, we should consider that tall vegetation, and potentially other things such as buildings may interefere with visibility. We can work this into our model by adding the height of the vegetation to the elevation surface. Because the vegetation map does not include roads, our construction of a egetation-height-offset layer should be merged with a layer of road cells, having an offset of zero.

Forested Areas

Reclass Forest to Height

Roads Excluded from Offset

Elevation Offset by Vegetation Height, Original Elevation

Corrected Elevation Model

Visibility Considering Veg-Heights, Before Offset

Designate Clearance

New Veg Offset Map

New Viewshed

New Viewshed on Airphoto