Lecture 5 Flashcards Preview

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Flashcards in Lecture 5 Deck (25)
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1
Q

GIS data sets often contain 3 key components:

A
  1. A spatial reference system
  2. Attribute data linked to the spatial features
  3. Metadata
    - if there is no Metadata either a good sign of not great data or you have to ask why they didn’t include it
2
Q

Accuracy Vs. Precision

A

Accuracy:the extent to which both attribute and positional data correspond to their real-world counterparts
eg, your road network data set has an accuracy of ±0.25 m – your data set is within 0.25 m of matching the real world road network

Precision: the exactness or repeatability of the measurements
-often described as the number of decimal places you can report your measurements to (compare 0.5 to 0.48739

3
Q

T OR F

high precision DOES NOT EQUAL high accuracy and the same reversed

A

T

▪ consider a car GPS system that boasts precise locating to less than 1 metre, but doesn’t have an accurate map of your location

4
Q

Types of errors when collecting measurments: 6

A

▪ attribute error (including logical consistency and completeness)
▪ positional error (x, y, and z)
▪ topological geometric error
▪ temporal error
▪interpretation error due to ecological fallacy
▪ error due to the modifiable areal unit problem

5
Q

2 common methods used to determine attribute accuracy:

A

1.random spot-checking
▪ in very large databases, checking every attribute is impractical; randomly choose 2% or fewer records and manually check and assess errors
2.spatial sampling
▪ use basic sampling techniques to choose how many records to check from each defined subset

6
Q

An error matrix quickly displays the error

A

▪ for categorical data (nominal or ordinal) assess errors in attribute data

7
Q

for finding error in interval and ratio data

A

the root-mean-square-error(RMSE) is commonly used

▪ RMSE compares the value of an attribute at a given location and compares it to the real world value at the same location
▪ consider a feature map showing leaf area idex (LAI)

8
Q

Errors:

  1. attribute logical consistency
  2. attribute and spatial completeness
A

1.
▪ in many cases, 2 or more people are involved in the collection of attribute data
▪ in this case, it is important that those collectors follow the same rules and logic for data collection to ensure that the whole dataset is consistent
▪ systematic errors occur when one set of data is consistently off of another set, usually because of some sort of user induced error

2.
▪ completeness is the degree to which the data exhaust the universe of all possible items
▪ a spatially complete data set covers all of the area of interest with the same level of detail
▪ hard to do since some locations are easier to access and collect data from
▪ a thematically (attribute) complete data set ensures that the data contain all the thematic information necessary for a given project and that it was collected with the same level of precision
▪ incomplete field, partial records, or missing records can wreak havoc with GIS analysis, especially if calculated statistics are involved

9
Q

topological errors

A

topological errors are usually created inside the GIS by the user as the geodatabase is being built

▪ a vector geodatabase is composed of lines and polygons – lines may not intersect or overshoot, and polygons may not close
▪ a fuzzy tolerance may be used to correct topological errors, but selecting the specific fuzzy tolerance is tricky, since too large a tolerance can join distinct but close features

10
Q

Shadow Map

A

A shadow map(slide 24)
-shows a map of error
-defines the confidence that you have in certain portions of a map
. using numbers or statistics to describe error is fine, but often visualizing those errors is a more effective way of describing them

11
Q

ecological fallacy

A

.the belief that all observations within an area will exhibit the same or similar values for a particular characteristic
-the characteristics of the group are the same for each individual in the group

12
Q

Modifiable Unit Area Problem

A

spatial data may be reported, mapped, and analyzed using enumeration units or districts of various sizes, including countries, regions, provinces, cities, census tracts, neighbourhoods, etc.
▪ when smaller areal units are combined into fewer but larger units,The variation present in the smaller units may decrease
. in general, the correlation between units increases as the size of the units increase, and it is possible for a researcher to manipulate the results of an analysis through this modifiable unit area problem

13
Q

GIS is simply a tool to help us ______, _____, _____, ______, and ________ various types of spatial data

A

store, organize, manipulate, analyze and present

14
Q

GIS DESIGN: 3 ESSENTIAL STEPS

A
  1. Identify Problem: every GIS application is designed to address a specific challenge or problem – for a GIS application to be successful, you must make sure that you fully understand the nature of the problem you are seeking to address
  2. Design and choose a data model: successful GIS applications model the part of the real world which is of interest to the problem under investigation
  3. Analysis Design: all GIS application are designed to allow users to explore a problem – the key to a successful analysis of a problem is the design of an appropriate framework for the analysis all GIS application are designed to allow users to explore a problem
15
Q

GIS DESIGN-Problem identification

A

.either structured or unstructured problems
.develop root definition after using “rich picture”
.identify what resources are available

16
Q

The rich picture

A

▪ the rich picture is a schematic view of the problem that your GIS will address, as it presents the main components of the problem as well as any interactions that exist
▪ a well thought-out rich picture provides a complete context for further work in the GIS and advancement of a project – it can be a difficult situation to find yourself deep into a project only to discover that you missed something important during the planning phase

17
Q

GIS DESIGN-Data Model

A

▪ the data model Links the real world to the modelled world you create in your GIS
.conceptual and physical model
-the Conceptual models adds spatial detail to the rich picture by including elements of spatial form and spatial process, while the physical model is concerned with how to represent the conceptual model within the computer

18
Q

the ________ model is a high-level view that describes what the problem is, what are the components of the problem, and how will these components work together and interact in the GIS

▪ the _________ model addresses how the data you need and analysis procedures will appear and operate within the GIS, including whether you will work in the vector or raster spatial models, or both

A

conceptual

physical
-▪ the physical model translates Conceptual model into GIS procedures

19
Q

GIS DESIGN- Analysis Design

A

▪ the primary method for spatial data analysis is known as cartographic modeling – essentially a set of tools that allow you to treat individual maps (spatial datasets) as variables in an equation
▪ this is also known as MAP algebra or mapematics

20
Q

MAP algebra or mapematics

A

the primary method for spatial data analysis is known as cartographic modeling – essentially a set of tools that allow you to treat individual maps (spatial datasets) as variables in an equation

21
Q

there are 4 stages to the development of a cartographic model:

A

1.identify the map layers of spatial datasets required

  1. use natural language to explain the process of moving from the available data to a solution
    - step 2 really deals with knowing and understanding the function of various commands/operations in GIS
  2. draw a flowchart to represent graphically the process of step 2
  3. annotate the flowchart with the commands necessary to perform these operations within the GIS
22
Q

Describe these:

  1. Union
  2. Intersect
  3. Symmetrical Difference
  4. Identity
  5. Erase
  6. Clip
A
  1. A or B
  2. A and B
  3. XOR
  4. Includes only one
  5. Take a piece
  6. Erase a piece
23
Q

Different Approaches to final implementation of GIS dESIGN: 2

A

tRIAL AND ERROR

Prototype approach

  • adjustable as you move forward
  • knowing when to stop development and lack of resources can be an issue
24
Q

some problems that cannot be planned for In GIS design: 3

A
  1. you may be limited by what data is available, and sometimes the available data is in the wrong format
  2. a lack of GIS knowledge can impose technical and conceptual constraints on a project
  3. users of the GIS frequently change their mind about what they want the GIS to do
    ▪ in many cases, you cannot control, or plan for, these problems, and they can slow you down or force you to rethink the entire project
25
Q

Risk Manaagement plans are often used before implemting a GIS design: 5 steps

A
▪ Step 1: identify the risks 
▪ Step 2: rate the risks
▪ Step 3: establish triggers 
▪ Step 4: identify mitigation action 
▪ Step 5: identify the owner of the risk