Mitchell: The ESRI Guide to GIS Analysis, ch. 1
GIS technology 30 years old
Good for making maps: but can do more than that: GIS Analysis
- maps (and GIS) don’t just show us what exists, the help us discover new things, help make decisions
- maps result from GIS analysis: have important impact (visual)
Why GIS might not be used:
- lack of data (changing rapidly, but still a problem)
- difficult software (but now easy interfaces; still complex though)
- lack of understanding about GIS analysis capabilities (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
- akin to the research process
1. Frame the Question:
- where are endangered ecosystems in Delaware County?
- where are potential recreational trail corridors in Delaware County?
- how can viable OWU food waste be efficiently distributed to area food banks?
- where does the food sold on campus come from, and what are the consequences of our consumption of these foods?
- what are the bird habitats on campus and how can they be enhanced?
- how can Delaware Run be restored in a campus-community-private sector collaboration?
- how can urban heat islands in central Ohio be assessed? Using what tools?
- how can drones be used with other remotely sensed imagery to assess environments?
- who is your audience? what is your final goal?
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?
- best to do solid research first then start to ask/bother people: they are apt to be more helpful if you come to them knowing something
- what is an endangered ecosystem? what are specific examples?
- what are the goals of recreational trails? what do they connect?
- how is food waste reuse assessed and how is it collected?
- 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? source? cost? compatibility?
- what data do you have to generate yourself? easy vs. difficult vs impossible
- what specific data will you need for your project?
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) generate a plan for distributing food waste from campus to area food banks
- ex) analyze the global impact of specific food consumption on campus
- what kind of GIS or other analysis will you need to understand for your project?
5. Look at the Results
- generate a map (with a database) and use it to present results
- ex) map of endangered ecosystems in Delaware Co: distribute to ??
- ex) map of potential trails in Delaware Co.: planners, bike clubs, etc.
- ex) a map that guides distribution of OWU food waste
- ex) map of the global impact of what we eat
- 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
Remember what I said about repetition of some concepts from reading to reading… as a way to assess concepts that are more important…
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, remotely sensed image, camera image (drone, thermal data)
Different data structures; can be related in GIS but generated differently and stored and processed differently.
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
Course Project Ideas
- apply Mitchell’s process of GIS Analysis to project
- good example of proposal format and content: Wetlands / Delaware State Park PDF
Below the fold find additional material from previous course projects.