GEO242.Lab3.SaveSnails
You will identify potential snail habitats at risk using vector overlay and
buffering. With the completion of this lab, you should be able to (a) perform
polygon overlay; (b) create buffer. This lab is adapted from "Mastering ArcGIS"
by Price.
1. Prepare data
- Download data for this lab.
- Extract the zip file.
- Copy all extracted files to your working folder properly named (e.g.,
E:\GEO242\Lab3).
- Double-click ESRI ArcMap Document SaveSnails.mxd. This will open
an existing map.
Three layers - Roads, Geology and Vegetation - should be shown in the map.
2. Identify potential snail habitats
It is known that this snail prefers lime soils (geology)
AND dense conifers (vegetation). Let's select lime
soils and dense conifers from existing layers.
- Open an attribute table of a layer Geology
- Select features from Geology where "NAME" is
'Upper Paleozoic' OR "NAME" is 'Madison Limestone'
using a query.
Selected features should be highlighted in the map.
- Open an attribute table of a layer Vegetation
- Select features from Vegetation where "COV_TYPE" = 'TPP'
OR 'COV_TYPE" = 'TWS'.
You will combine lime soils and dense conifers using
polygon overlay, specifically Intersect method. Intersect creates a new feature
from the common areas of any two selected features.
- Open ArcToolbox window
- Analysis Tools > Overlay > Intersect
- Choose Geology and Vegetation from Input Features,
and save the output feature class as SnailHabitat.shp in your working
folder. See the image capture for verification. If
you keep getting an error in intersection operation, do
this.
- Open the attribute table of a layer SnailHabitat, and
browse what part of the study area has Upper
Paleozoic and coverage type TPP using a record selector (the leftmost
bar in the attribute table window). Overlay combines geometry and
attributes.
- Clear the selection.
- Save the map as SnailHabitat.mxd in your working
folder. It is always a good habit to save a map as frequently as possible.
3. Identify potential snail habitats at risk
To prevent snail death on the major roads, the Forest
Service biologist is considering thinning the tree stands within 200 meters of
the roads, which might keep the snails away from the roads.
- Select roads from the Roads layer, using the
expression "TYPE" = 'P' OR "TYPE" = 'S'. This will select the primary and
secondary roads.
- In ArcToolbox, Analysis Tools > Proximity > Buffer
- Choose Roads for Input Features, save output feature
class as Roads_Buffer.shp in your working folder. Type 200 in the Distance
input box. Choose ALL for dissolve type. See the image
capture for verification.
- Turn off the Roads layer, so it won't block the
Roads_Buffer layer.
Let's combine Roads_Buffer and SnailHabitat using overlay
(intersect), which will help the geologist estimate stands to be cleared and the
percentage of snails to be affected.
- In ArcToolbox window, Analysis Tools > Overlay >
Intersect
- Choose Roads_Buffer and SnailHabitat from Input
Features, and save the output feature class as SnailHabitatAtRisk.shp. Click
here if you're not sure what to do.
4. Make a map showing the stands to be cleared (SnailHabitatAtRisk)
and potential snail habitat
- Submit the map in image file to D2L dropbox. Make
sure the map include at least two layers (SnailHabitatAtRisk and
SnailHabitat) where SnailHabitatAtRisk looks more pronounced than
SnailHabitat. The percentage of snail habitat to be affected by stand
clearing should look about 20%.