Due date (at the beginning of your lab section):
AA, AB, AC on November 12
AD, AE, AF on November 13
To help you understand this lab, please be familiar with the
following:
How
To Save Your Work
What
to record in a process diagram
Exploring
Geographic Information Systems (Chapter 6)
Distance
Transformations and Buffers
Attribute-based
operations
Combination
of Attributes
Completed answers to the questions in Parts A and B and process diagrams of the steps performed in Part B. Blank diagrams are not provided for this. Please answer the questions in your own words.
1. Please read and make sure you understand how to save your work. 2. If you haven't already done so, create a working folder. 3. Start ArcMap with a new empty map. 4. Load the "Spatial Analyst" extension (Tools -> Extensions). 5. Open the Spatial Analyst toolbar (Tools -> Customize -> Toolbars). 6. Set the working directory to your working folder. 7. Add the following raster (GRID) themes:
- p:\geog460Au03\Data\ex4\strmgd
- p:\geog460Au03\Data\ex4\roadgd
8. Add the following feature vector layers (shapefiles):
- p:\geog460Au03\Data\ex4\vbuf200.shp
- p:\geog460Au03\Data\ex4\bi_streets.shp
9. Finally, save a copy of the current project as a new project in your working folder. Use a name that you will remember (perhaps Ex4).
Distance to and from various objects is often an important concern in land use planning and site suitability studies. Foresters are now required to observe "setbacks" from streams in order to protect fish habitat. Developers often want to build commercial sites close to major streets and highways. These are examples where it is necessary to know distances from identified objects. In this exercise we will study distances from both roads and streams on Bainbridge Island. We have made raster themes of roads (rdgrd), and streams (strmgd). You will create buffers around these objects and study the relation between these.
The "Distance" operations will create a floating point grid (no table to open, but the Identify tool still works) measuring from ALL cells with a "non-null" value. It will calculate nearest distances from every cell that is not "no data" to every other cell in the grid. You will want to pay attention to the trigonometry of raster cells to understand how the distances were derived and the limitations on their use.
| 1. | Select and highlight the theme 'roadgd'. |
| 2. | Select: Spatial Analyst -> Distance -> Straight
Line (Leave the cell size as is, Do not set a maximimun distance or create direction or allocation grids.) . |
| 3. | Look for the result theme in the table of contents called 'Distance to roadgd'. |
| 4. | Display and select (check box) the theme 'Distance to roadgd'. |
| 5. | Bring the 'roadgd' theme to the top of the Table of Contents (click and drag it on to the top of the Table of Contents). |
| 6. | Use the Zoom and Identify tools to examine the values of the resulting grid. (notice the options of layers in the identification results window). Zooming in very close to the end of a road will help you answer these questions. |
Question A1: What cell value is given to a non-road
cell with a whole side adjacent to a road?
Question A2: What value is given to a non-road cell on
a diagonal from a road? [A cell that only touches a road cell
on the corner.] (Ho do you explain this value, geometrically?)
| 7. | Select Spatial Analyst > Raster Calculator. |
| 8. | Enter the selection for all cells within 200 feet of a road:
( [Distance to Roadgd] <= 200) Click Evaluate. The result will be called Calculation. |
| 9. | Rename 'Calculation' as 'roads200'. |
| 10. | Hide (remove check mark) for 'Distance to roadgd'. |
| 11. | Display 'roads200' underneath 'roadgd'. |
Question A3: How many cells are in the 200 feet buffer?
FYI - the theme 'vbuf200' was created using the 'Buffer Wizard' (Tools > Buffer Wizard).
12. Display 'vbuf200' on top of 'roads200'.
13. Display 'bi_streets' on top of 'vbuf200'.
14. Display 'roads200 on top of 'vbuf200'.
Question A4: Describe and explain the differences in the space (shape and area) identified as the buffer zone by these two buffer methods (raster and vector).
| 1. | Select and display the layer 'strmgd'. |
| 2. | Select: Spatial Analyst > Distance > Straight Line. Leave settings as default. This will produce the result theme 'Distance to strmgd'. |
| 3. | Select: Spatial Analyst -> Raster Calculator. Compose
the following argument in the command box: Diff = ( [Distance to Strmgd] - [Distance to Roadgd] ) Click Evaluate. Close the Raster Calculator window. |
| 4. | Select and display 'Diff'. |
| 5. | Select Spatial Analyst > Raster Calculator. Enter the equation: Thatmap = ( [Diff] > 0 ) Click Evaluate. |
Question B1: Draw a process diagram of these three operation steps.
Question B2: How do you interpret the results of the calculation (called "Thatmap")?
Question B3: What would be a more descriptive title for "Thatmap"?