GEOG 385.02/GTECH 785.02  GIS APPLICATIONS IN SOCIAL GEOGRAPHY Back to MP home page

### MASTERY EXERCISE 1. RASTER AND VECTOR REPRESENTATIONS OF SPACE AND FEATURES

 Start: 2/11 Due: 2/18 Data: Print this page and pick up Handouts A and B. Turn In: Handouts and answers to the questions below

Using Handouts A and B, fulfill the assignment following the instructions below and answer the questions in the space provided. Answers should be short (one word or 1-2 full sentences). Write clearly please. If you do not have enough space, please attach an additional page.
Handout A.
1. For each feature shown on the vector map, prepare the necessary information to describe this feature:
1.1. Determine Feature ID, Feature Type (point, line, or polygon), and number of its constituent elements (number of points in each feature).

• Assign sequential numbers (clockwise from the upper-left) to all points that make up this feature. Note that within each feature, points are numbered starting with 1.
• Determine approximate (x,y) coordinates of each point ONLY in the following features: Path and Birch Stand.

1.2 Include this information into your description of features and present it in the following table:

 Feature: Path Feature: Birch Stand Feature ID: Feature ID: Feature Type: Feature Type: Number of points: Number of points: Points: X: Y: Points: X: Y:

EXAMPLE:

 Feature: Fountain Feature ID: 11 Feature Type: Point Number of Points: 1 Points: X: Y: 1 0.5 4.5

2. Present the same portion of the Central Park in raster format using the raster grid provided. Assume that coordinate origin is in the lower left corner as it is in the vector format.
2.1. Shade pixels with non-zero attribute values with different colors (make sure that you can see the values): 11-red    2-yellow    5-blue    7-green

2.2. What is the total number of attribute values in this raster file?____________

2.3. Vizually compare both types of representations of Central Park. What format (raster or vector) suits better for representing spatially discrete features?

2.4. If you used 100 by 100 raster grid instead of 8 by 8 grid to show the same area, would the representation of features in raster improve? Why?

Handout B.
3. Examine raster digital elevation model of the area. North is on the top, South is on the bottom.

3.1 Determine whether the following statement is true of false:
In general the elevation increases from South-West to North-East.

True    /    False  (circle one answer)

3.2 The maximum elevation in this image is__________ ft.

3.2 The number of pixels with maximum elevation values is _______.

4. Convert this raster surface into vector contour lines. Contour lines connect points with equal elevation. Draw only THREE contour lines using the vector coordinate system provided. These contour lines should be at the elevation of 0, 1, and 2 feet. Label the countour lines with these values.

NOTE: When converting raster values to vector format, remember that a vector point is created in the center of the pixel.

4.1 Do any vector features or values exist between the contour lines? Why?

4.2 If you had a raster grid 100 by 100 instead of 8 by 8, it would show finer variation in elevation in this portion of Central Park. Would your resulting contour lines be smoother or rougher?

4.3 Which format (raster or vector) is better for representing continously changing phenomena such as elevation? Why?