sources of data

Question 1

What are the two main forms of geographic data?

Answer 1

Analogue data (hardcopy) and digital data.

Question 2

Give three examples of analogue geographic data.

Answer 2

Paper maps, tables of statistics, and hard copy aerial photographs.

Question 3

What are some sources of digital geographic data?

Answer 3

The internet, digital imagery, and data collection devices.

Question 4

What is the main advantage if all data were in the same format, type, scale, and resolution?

Answer 4

Encoding would be simple.

Question 5

Differentiate between primary and secondary data sources.

Answer 5

• Primary data sources: Collected in digital format specifically for use in a GIS project.
• Secondary data sources: Existing digital or analog datasets originally captured for another purpose, requiring conversion to a suitable format for GIS.

Question 6

What are the two most common ways to obtain raster data?

Answer 6

Aerial photography and satellite remote sensing.

Question 7

sources of raster data

Answer 7

1. remote sensing satellite data
2. space shuttle images
3. digital elevation model
4. aerial photographs
5. derived raster products

Question 8

sources of vector data

Answer 8

GPS ans ground survey data
converted and derived products

Question 9

list the 7 data capture and input methods

Answer 9

1. photogrammetric compiltion
2. digitizing
3. map scanning
4. entry of coordinates via coordinate geometry
5. conversion of existing digital data
6. satellite data
7. document scanning

Question 10

3

The pre-processing of GIS data i.e. data editing can be grouped in to?

Answer 10

• Detecting and correcting errors
• Reprojection, transformation and generalization.
• Edge matching and rubber sheeting.

Question 11

3

sources of data errors are

Answer 11

• Errors in data sources: Issues like map inaccuracies or printing errors.
• Encoding errors: Scanning, digitizing, or typing mistakes.
• Transfer and conversion errors: Data loss or corruption during format changes.

Question 12

error detection methods in attribute data editting.

Answer 12

checking for;
1. Impossible values: Identifying values outside an expected range.
2. Extreme values: Spotting outliers.
3. Internal consistency: Checking totals and averages for accuracy.
4. Scatter diagrams: Highlighting correlation inconsistencies.
5. Trend surfaces: Identifying outliers significantly different from the data trend.

Question 13

detecting and correcting errors in raster data

Answer 13

1. Filling holes and gaps
2. Edge smoothing
3. Deskewing
4. Speckle removal
5. Thinning
6. Clipping
7. Rasterization

Question 14

common errors and corrections in vector data

Answer 14

1. Pseudo nodes
2. Dangling nodes
3. Label errors
4. Sliver polygons