Mitchell: Ch. 1: Introducing GIS Analysis

GIS technology 30 years old

Good for making maps: but can do more than that: GIS Analysis

Delay in the use of GIS analysis

• Lack of data (changing rapidly, but still a problem)
• Difficult software (but now easy interfaces; still complex though)
• Lack of understanding about GIS analysis (the book)

• where are things in geographic space?
• mapping variations in amount: least and most
• mapping density
• finding what is inside
• finding what is nearby
• mapping change

What is GIS Analysis?

GIS Analysis as a process

• simple visual analysis to complex digital modeling

1. Frame the Question:

• where are endangered ecosystems in Delaware County?
• where are potential recreational trail corridors in Delaware County?
• how can we understand the tangible state of environmental justice in Delaware County OH?
• who is your audience? what is your final goal? What is your final product?

2. Understand your Data

What is the context of your question? who are the experts? literature, people

What do you have to know about the context of the question to answer it?

• what is an endangered ecosystem? what are specific examples?
• what are the goals of recreational trails? what do they connect?
• what is Environmental Justice and what kind of data helps us understand it?
• what or who can help you to understand the issue: literature, people

3. Choose a Method

• what data is available to help answer your question? cost? compatibility?
• what data do you have to generate yourself? easy vs. difficult vs impossible

4. Process the Data: specific analysis

ex) generate endangered areas by comparing areas defined as important ecosystems to their closeness to recent development

ex) generate potential trails by generating important points and areas to connect; and determining feasible paths between those points; relate potential trails to property ownership and other factors

ex) Environmental Justice?

5. Look at the Results

• generate a map (with a database) and use it to present results
• map of endangered ecosystems in Delaware Co: distribute to ??
• map of potential trails in Delaware Co.: planners, bike clubs, etc.
• Environmental Justice?
• vital part of the process: communication and advocacy

Simple in concept; complex in application!

Understanding Geographic Features

We reduce the complexity of the real world in order to collect data and map it

A feature: “something inherent and distinctive”

Types of features (mappable data)

1. Discrete Features: at any location, the feature is there or is not there

• point, line, and area example: p. 12
• corresponds to vector data structure in most GIS programs

2. Continuous Features: feature is everywhere in varying amounts

ex) temperature
ex) elevation
ex) soil or bedrock (Delaware Data)

3) Features Summarized by Area: census or count data

• define an area; count features in the area; assign total to the area
• know how many features in an area, but not where they are in the area
ex) US Census data, animal census

Two Ways of Representing Geographic Features

1) Vector: points, lines, and areas

• each point has a unique location in a coordinate system: latitude/longitude
• points connect to make lines
• series of points, connected to make lines, which close are areas

2) Raster: grid of varying resolution with cells

• air photo

Raster vs Vector: very different data structures; can be related in GIS but generated differently and stored and processed differently.

Map Projections and Coordinate Systems

Review from Geog 222 or 353

Coordinate systems: based on the idea of a graph

• locations in geographic space: x, y
• latitude longitude vs state plane coordinate system
• coordinate layers of GIS information

Map projection

• 3D earth to 2D map
• distortions inherent in process (shape, area)
• distortions less evident at detailed scales
• but GIS layers must have same map projection or will not align properly

Understanding Geographic Attributes

A geographic feature (point, line, area) has one or more attributes

ex) area is a vernal pool, it is 1 acre, it is on private property (3 attributes)

Types of attribute values

categories: qualitative
ex) vernal pool (area) vs river (line)

ranks: quantitative with order
ex) water quality: high, medium, low

counts and amounts: quantitative, total numbers
ex) 35 robins in one nature reserve, 67 in a second reserve

ratios: relationship between two quantities
ex) people per household in census tracts in Delaware county

data tables: the ‘database’ or spreadsheet where the feature attributes are found
ex) select all properties in Delaware County that are residential land use
ex) calculate and summarize the total value of all properties a proposed
trail crosses

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