Spatial data quality and uncertainty

Question 1

what is uncertainty?

Answer 1

difference between the contents of a dataset and the phenomena that the data are supposed to represent

Question 2

what are some sources of uncertainty?

Answer 2

• users (variation in understanding how a real thing differs from its representation)
• units of analysis (i.e. how do u measure health?)
• proxy and indirect indicators (i.e. judging income based on home location)
• geographic phenomena
• GIS data model (i.e.raster vs vector)

Question 3

Who sets standards for data quality?

Answer 3

• International Standards Organization (ISO)

- governemnt legislation (i.e. US national map accuracy standards, Canada national topographic database standards)

Question 4

how is data quality differnt from the user and the producer perspective?

Answer 4

producer: degree to which data in a dataset conforms to the capture specification and to product specifications for the dataset (internal data quality)
- user: data quality=fitness for purpose of data. external data quality

Question 5

What are some elements of spatial data quality?

Answer 5

• completeness (i.e. omission)
• logical consistency (does it make sense topologically, conceptually)
• positional accuracy (i.e. location of lake in feature class vs location in a TIFF image)
• thematic accuracy
• temporal quality

Question 6

What are errors?

Answer 6

• deviations between measured value and its true value

- classes: human, systematic (biases in equipment use, defects in measuring equipemtns), random errors

Question 7

Are accuracy and precision the same thing?

Answer 7

• accuracy: how close the recorded values are to “true” values.
• precision: how exact data measurement and storage are (i.e. # of decimal place)

Question 8

What document sets standards for measuring and evaluating quality from a producer’s perspective?

Answer 8

-ISO 19157

completeness, logical consistency, positional accuracy, thematic accuracy

Question 9

Explain positional error

Answer 9

• error in locational coordinates (x,y)

- Root Mean Square error: tells us how far points are from their true location on average

Question 10

What are some sources of positional error?

Answer 10

• map projection, datum
• improper representation of objects or phenomena (i.e. boundaries)
• equipment errors
• human errors (i.e.bad sampling procedures)
• media related (i.e. bad source quality like CanVec data)

Question 11

How can we determine if the data we use is good enough?

Answer 11

• check metadata!!
• consider validity of authors
• compare with the real thing

Question 12

Explain map topology

Answer 12

• temporary relationships between FCs or shapefiles within a ArcMap edit session
• i.e. reshaping polygon edges

Question 13

Explain geodatabase topology

Answer 13

• used to check data integrity relative to the rues and FCs that are selected by the geoDB designer
• rules govern relationships between features within an FC or between several FCs
• topology rules are saved as table object inside feature dataset
• relationships in each rule are checked against the participating data sets