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Constraint Analysis in GIS. As demonstrated through the derivation of sites appropriate for a Waterpark Seamus McDougall Ian McIlravey Keerthika Logendran Andrew Thompson. Background.
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Constraint Analysis in GIS As demonstrated through the derivation of sites appropriate for a Waterpark Seamus McDougall Ian McIlravey KeerthikaLogendran Andrew Thompson
Background Waterparks exist in a variety of sizes. They range from small indoor operations of a few acres (often incidentally associated establishments including pools and hotels), up to to large destination parks which reach over 100 acres in size. In the middle are smaller parks of about 3-8 acres which also function somewhat as destinations in their own right. For this exercise it was assumed that the purpose was to find a site suitable for a fairly large, regional-scale waterpark (likely closer to the 100 acre end of the spectrum if possible, in order to ensure a successful operation).
Initial Constraints • In the initial stages of the constraint analysis, the obvious constraints were identified first. These were legal or physical impediments which directly precluded the location of a waterpark on said sites. They were: • The legally-mandated 120 m buffer zone around wetlands • Waterbodies/features • Cemeteries • Land used for: • Industrial/resource purposes, • Government/institutional buildings • Commercial purposes • Residential purposes • Parks and recreational uses • Transportation (roads and railways) • Pipelines and utility corridors • Forested areas - Any land already covered by a building
Proximity-Based Constraints • Some areas must be avoided to degrees beyond simply not locating within them. This is due to externalities which could result from different land uses being located too closely together. It is for this purpose that buffers are imposed around things which one would not wish to have nearby to a waterpark. These were identified as being: Buffers: • Residential areas 500m and 1000m buffer (due to noise and aesthetic concerns on the part of residents) • Industrial and resource areas 500m (due to noise, pollution, and aesthetic concerns on the part of the park) • Cemeteries 500m and 1000m (out of respect for their visitors) • Waterbodies 100m (due to concerns about the suitability of a waterpark on a shoreline, related to both ease of construction and the logic of having two water sites adjacent to each other)
Desirability-Based Constraints • Some areas are uniquely better-suited to hosting a waterpark than others. This is as a result of their having qualities desirable for a successful business. It is handy to identify or buffer these areas. Once this is done one will have desirable areas selected; by subtracting the constrained (undesirable) areas from the desirable ones one will be left with only sites that are both desirable and unconstrained. • For a waterpark desirable site qualities identified were: • Openness (of space, i.e. no other buildings) • This ought to be mostly taken care of by initial and proximity-based constraints, which chip away unsuitable areas. However, there is a building points layer which could contain important info which could not be taken into account by blacking out or erasing polygons. • Accessibility (evaluated in two ways): • Firstly by using a 5 km buffer around freeway paths, in order to select areas simply proximate to freeways (this meant that all remaining areas were de facto too far away in any scenario, for our purposes); and • secondly by using accessibility by freeway as a desirable quality. This was done by buffering freeway interchanges, at both 1 and 2 km values, in order to determine more precisely which sites would take longer to drive to. • 750m buffer on small interchanges in case land is totally unsuitable near freeway/freeway interchanges
Therefore: • the best areas in which to locate a water park are those that are within the 5km freeway buffer • within this zone it would be best to locate within the more-restrictive freeway interchange buffers, which are specifically more accessible by car • it is further necessary that sites within these bounds not intersect with any of the constraining land uses (industrial, waterbodies, wetlands, parks and rec, etc.) • The sites left at the end of this process of selection and removal will be the best, most accessible, and least disturbing of all possible options within York Region
There rests one more variable to consider when selecting for the site of the park. It is slope. • The easiest way to evaluate sites based on this criterion is to map it out; for this project we chose to group values from the “slopes for soil” layer which we decided to be medial; these ranged from 0.2 to 7.5, with differences between classes never exceeding 2.3 • A binary colour scemme was incorperated into the slope constraint map to simply illistrate usable and unusable slopes. This would make interperating slopes easier for a untrained map user who is selecting the site. • Then, one can see, using simultaneous map display or intersect, which of the previously-identified desirable areas has the most appropriate slope conditions • This can aid in a final decision about where would be best for the park. It is not, however, an absolute restriction, as slope conditions can be overcome using various construction techniques. However, for practical purposes, it would be good to look at for reasons of convenience (both for developer and patron) and cost. It is for this reason that its analysis is left to the end, after any other constraints and desirable qualities have been identified and mapped.
Final notes * • It was noted in the specifications for the project that waterparks were to avoid CBDs (central business districts). • Though this was not specifically analysed it was assumed that the constraining of various land uses and the buffering of residential areas were adequate to eliminate sites proximate to CBDs from consideration. • This is due to the outward-spreading nature of urban areas, which tend to have CBDs surrounded by residential/commercial/industrial lands. York is an outlying, suburban region, so the problem was thought to be especially inapplicable. • Small watercourses were not considered in this analysis; they occurred too frequently over the study area to be a valid constraint. In the map layer, all polylines are digitesed as the same width; therefore identification of problem streams (based on exceptional characteristics, i.e. size) was not possible. • Furthermore, during project construction; culverts, diversions, and other workarounds can be preformed on a case-by-case basis.
Constraint Analysis Process Flowchart + + = The Only Remaining Land Will Be Suitable for Waterparks
