Understanding GIS. David Smith
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Название: Understanding GIS
Автор: David Smith
Издательство: Ingram
Жанр: Программы
Серия: Understanding GIS
isbn: 9781589485273
isbn:
According to Villaraigosa, “The plan provides a 25- to 50-year blueprint for transforming the city’s 32-mile stretch of the river into an ‘emerald necklace’ of parks, walkways, and bike paths, as well as providing better connections to the neighboring communities, protecting wildlife, promoting the health of the river, and leveraging economic reinvestment.”
Although the 2005 master plan identified some of the most obvious areas for large-scale regional redevelopment along the river, it stopped short of identifying smaller (and more affordable) neighborhood projects; that work would require a more involved study. With thousands of land parcels strung out along the river, identifying the best places for park development is like looking for a needle in a haystack. Many factors come into play, among them current land use, demographics, and accessibility.
In the years since the plan’s completion, the city has created a website (figure 1-3) that encourages people to learn about (and participate in) the latest developments related to its landmark resource. The website, at www.lariver.org, contains links to many resources about the river and its watershed, including scientific studies and recreational opportunities. If city leaders can find the resources and a motivated citizenry keeps up the pressure, a renaissance will transform growing stretches along the river into real versions of the revitalization effort’s artists’ renderings (figure 1-4).
Figure 1-3. The Los Angeles River Revitalization website contains links to information about the river and its watershed.
Figure 1-4. The Los Angeles River Revitalization website contains artists’ renderings (A to C) of a rejuvenated river corridor.
Here’s where you pick up the thread in this book. You’ll use the city’s real need for river redevelopment as a launching point for a park siting analysis using a geographic information system (GIS). A GIS is ideal for this type of decision-making, because it allows you to analyze large amounts of data in a spatial context. In this book, you’ll spend a lot of time with ArcGIS Pro software, and by the end you’ll have completed a project from scratch. Along the way, you’ll gain an excellent grasp of what a GIS can do.
You’ll be assuming the role of a GIS analyst for the City of Los Angeles. So what exactly does a GIS analyst do, and how is that job different from other jobs that also use GIS software? Table 1-1 defines some of the various roles that a typical GIS operation might establish to accomplish its work.
| Table 1-1. GIS roles | |
| Editors | People who create, update, and correct spatial data and its attributes (statistical and descriptive information). |
| Cartographers | People who make and publish maps and solve information design problems. |
| Analysts | People who query and process geographic data to solve analytical problems. |
| Programmers | People who implement custom GIS functionality by developing scripts and applications for specific procedures. |
| Managers | People who oversee staffing and equipment, database design, workflow, new technology, and data acquisition. |
The central work in this book is analytical. Your main focus will be on using ArcGIS tools and methods to find the most park-suitable land within a study area, but there is preparatory work to do before the analysis proper, and there are results to interpret and present afterward. This book has two goals. One is to present a comprehensive approach to geographic problem solving. We want to help you develop skills, habits, and ways of thinking that will be useful in projects other than this one. The second goal is to teach you how to use ArcGIS Pro software. These goals are mostly complementary. ArcGIS is a big system, however, and it wouldn’t be realistic to try to cover all that it can do in a single book. Our principle has been to teach the software in the service of the project and not otherwise. You’ll delve into many aspects of ArcGIS Pro—editing, modeling, and cartography, among them—but there are other aspects that we won’t use, or will only touch upon lightly, because they aren’t strictly relevant to our needs. We might say (with apologies to Waldo Tobler)1 that everything in a GIS is related to everything else, but some things are more closely related to analysis than others.
Frame the problem
The first step in the geographic approach to problem solving is to frame the problem. What that means, first, is coming up with a short statement of what it is you want to accomplish. For this project, you want to find a suitable site for a park near the Los Angeles River.
Once you have the statement, you can begin to tease out its ambiguities. What factors make a site “suitable”? In this case, the city council has already established a concise and fairly specific set of guidelines.
Park guidelines
1.On a vacant parcel of land at least one-quarter acre in size
2.Within the Los Angeles city limits
3.As close as possible to the Los Angeles River
4.Not in the vicinity of an existing park
5.In a densely populated neighborhood with lots of children
6.In a lower-income neighborhood
7.Where as many people as possible can be served
This list limits the scope of your inquiry, but it’s far from a complete breakdown of the problem. Some of the guidelines are specific, but others are vague. Familiar concepts are sometimes the hardest to pin down. For example, what income level should count as “lower income”? How are the boundaries of a “neighborhood” established? You can’t solve the big problem until you’ve solved the little problems buried inside. Usually, however, it’s not possible to address (or even foresee) all the little problems ahead of time.
Data exploration influences the framing of the problem. Do you have income data on hand? If so, is it for individuals or households? Is it average, median, or total? To the extent that the questions themselves are indefinite (What is lower income? How should it be measured?), the data you have available will help shape the answer.
Analysis also influences the framing of the problem. Given that you want a quarter-acre tract of vacant land, what do you do about adjacent lots? Is there a tool to combine them? If so, does using it have unanticipated side effects, such as a loss of information? Your data processing capabilities (and your knowledge of them) may determine how you define a “one-quarter acre parcel.”
Even the results of an analysis influence the framing of the problem. Suppose, after having carefully defined the guidelines, you run the analysis and don’t find any suitable sites. Do you report to the city council that there’s just no room for a park? More likely, you’ll change some of your definitions and run the analysis again.
Framing СКАЧАТЬ