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Tracy K. Holloman EVSC 468 March 18, 2003

Proximity Analysis. Tracy K. Holloman EVSC 468 March 18, 2003. Topics. What is Proximity? Tools Select By Location Description Buffer Wizard Description Advantages of Different Methodologies Capabilities Sensitivity Analysis Conclusions Demonstration. What is Proximity????.

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Tracy K. Holloman EVSC 468 March 18, 2003

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  1. Proximity Analysis Tracy K. Holloman EVSC 468 March 18, 2003

  2. Topics • What is Proximity? • Tools • Select By Location Description • Buffer Wizard Description • Advantages of Different Methodologies • Capabilities • Sensitivity Analysis • Conclusions • Demonstration

  3. What is Proximity???? • CLOSENESS • Within the vicinity of a certain feature or landmark • Importance: Essential to determining whether a certain feature will impede your ability to travel to a specified location • Best route and location determination

  4. Tools For Determining Closeness • Select By Location • Buffer Wizard

  5. Select By Location • Uses Standard Query Language to describe an association between two Layers • Selects a set of features that fall within a specified distance of the pre-determined feature class • Results=Highlights selected features, does not degrade the integrity of the original data in any way

  6. Select by Location PROCEDURE

  7. STEP 1: Choose selection: Select Add to Remove Or Select from current Selection (second level of selection)

  8. Step 2: Choose the layer you would like to select features from, add to, remove from, or select from currently selected features

  9. Step 3: Choose the Relationship Between your two layers: Intersect Are Within a Distance of Are Completely Within Completely Contain Have Their Center in Share a Line Segment With Touch the Boundary of Are Identical to Are Crossed by the Outline of Contain Are Contained By

  10. Step 4: Choose the Second layer that you would like to use in conjunction with your initial layer

  11. Step 5: Choose the distance and units you would like your buffer to include

  12. Step 6:Apply!! Results = Teal

  13. What is a Buffer? • An object created that embodies components of existing objects • Works well with impact analysis • Both raster and vectordata sets can use buffering capabilities • 3 types: causative(extent of toxic spill),mandatory(deals with either land use or zoning),arbitrary(used in conjunction with sensitivity analysis)

  14. Buffer Wizard PROCEDURE

  15. Step 1: Select the layer you would like to apply the buffer to

  16. Step 2: Implement the distance your buffer will embody

  17. Step 3: Choose the name you would like for your output Shapefile NOTE: You can choose to dissolve barriers or leave them as a means of distinguishing individual components

  18. Step 4:Hit Finish Buffers = Brown!!

  19. Advantages/Disadvantages of Each Methodology • Select by Location does not disrupt the original data, it simply selects the features meeting a certain standard and highlights them • Buffer Wizard allows creation of a new layer which can be edited—not simply a graphic display

  20. What can these tools do?? • Accessibility: the size and closeness of a given activity system with respect to a certain zone • Choice: allows routes to be chosen on basis of connectivity and integration • Safety and Security: enables one to determine the area affected by pollution or a spill situation • System management: determine routing to insure efficiency and maintenance of population needs

  21. Analysis • To demonstrate the functions available through GIS, I downloaded several shapefiles containing roads, railways, landmarks and hydro features within Chesterfield County Virginia • Lets determine the railways that lie within a 1 mile distance of landmarks

  22. Methodology • Add both the rail and landmark layer to the ArcMap Data Frame • Choose the Select by Location menu • Select Features from the Rail Layer that are within a distance of 1 mile of the landmark layer • Hit apply

  23. Methodology Continued • Once the select by location has been applied selected features will be highlighted in teal • To see the actual features that were highlighted right click on the Rail Layer • Open the Attribute Table • Hit Selected Features to obtain a complete listing of the selected features

  24. Road Placement with Respect to Landmarks • Next, I would like to examine how Buffer Wizard could be used to examine Road placement with regard to Landmarks • Addboth the Landmarks and road layers to the Data Frame • To begin with I selected Buffer Wizard • I would like to buffer features within the Landmark Layer • I wanted a .25 mile buffer around this layer to determine roads within close proximity

  25. Note: Buffered areas appear brown by default

  26. Hydrology within .5 mi. of roadways • How could stream networks influence roadways? • Could flooding plague certain areas? • Add both the hydro and road layers • Choose Select by location • Select features from the Hydro Layer that are within a distance of .5 mi. of the Roads Layer • Features Selected are highlighted in teal

  27. Note: numerous hydrological features are within .5 mi of roadways

  28. Sensitivity analysis • Perhaps by manipulating the distance between the hydro layer and the road layer we can get a better feel for their relationship • Choose three distances, say .25, .5 and .75 miles • Determine the number of hydro features embodied by each to see if parameter variation is in fact important

  29. 1386 Out of 1562 hydro features are highlighted when the buffer is .25 mi.

  30. Note: 1482 out of 1562 hydro features highlighted when buffer Is .5 mi.

  31. Note: 1516out of 1562features in hydro layer selected when .75 mi. buffer is employed

  32. Variation • Inconsistencies: data exploration to determine “key” sensitive parameter = necessary • Consistency: robust data • Therefore, the further away from the hydro layer you go the more roads are encapsulated • Thus, determination of the exact flooding extentcertain frequency storms could induce should be determined to quantify the precise number of roadways affected

  33. Conclusions • Select by Location and Buffer Wizard are vital components of proximity analysis • Both can give you graphical output, however, buffer wizard enables the creation of new shapefiles based on results • Sensitivity analysis is key to determining the extent to which parameters affect the overall outcome of analysis

  34. Demonstration • Roads within a .25 mile distance of landmarks: A--using select by location B--using buffer wizard

  35. Questions

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