Vector analysis Flashcards
What are the 3 parts to a query?
Field name ex. volume
Relational operator (bigger than, less than, equal to) ex. greater
value ex. 250m3/ha
What are boolean operators?
used to carry out a complex query -And -Or -Not to refine search
What is the arithmetic calculation feature?
Applies a formula to a numeric field (similar to excel but different interface)
What is a the statistics function?
provides a temporary pop up table with typical statistical parameters and plots data in a histogram.
What is the function of the summarize feature?
creates a data table that you control the field output of. table is permanent.
What are the 2 options when you right click a field name?
Summarize or Statistics
What are the data classification schemes?
- natural break
- quantile
- equal interval
- user defined
What are the max number of classes you would display on a map?
5-7 due to color overload
What must you ensure that you do when relating the attribute table to outside tables in arcGIS?
- You must make sure that you are in the GIS attribute table when you make the join or link.
What is the euclidean distance function?
(Straight line distance)
What does geometric distance function give you?
line length (perimeter)
How would you calculate area?
use the geometric area function
What is important to remember about overlays and area?
Do not trust the area after you have performed an overlay
create your own column called ha. and use calculate area function.
What is the select by location query?
- feature selected based on relation to other features by comparing two themes.
- Target layer - features selected
- outside source layer - basis for selection
- ie. Within a distance of, within another feature.
Some relationships
- intersect
- contain
- within a distance of (within a buffer)
What is a buffer? **
- creates a new data layer
- creates polygons defined by a cerrtain distance from select features. (ex. wildlife tree buffer)
What are the 3 buffer types?
- single (simple) buffer
- multi rings
- variable widths - defined by values in field (fish streams vs non fish)
What is the purpose of the dissolve feature when overlapping buffers?
merges the overlapping buffers into one (forester should use this function)
What is the point of an overlay?
- combine 2 layers
- creates a new data layer
- both linework and attributes
What are the 5 types of overlays?
Clip Intersect Union Update Erase
Describe the “clip” method of overlay
- Area defined by the clip overlay theme
- 2 map layers are combined to Give a mini version of the original map
ie. what forest is contained within a cutblock (input “dough” output “cookie”.)
Describe the intersect type of overlay
- Area displayed is where the 2 maps overlap
- table contains all fields from both themes
- ex. landowner and forest
Compare clip and intersect
- similar on spatial side
- clip only displays attribute data from the input (cookie dough) map
- intersect contains attribute data from both maps
What is the union method of overlay?
- area is the total area of both (= COMBINED AREA = OR)
- table contains fields from both themes
What is the difference between intersect and union?
- intersect only uses coincidence space
- union keeps all space from both maps
What is another term for query?
select by attribute
What is the update overlay type?
- updates features
- fields in both layers have to match
- ex. new cutblock supercedes forest theme
What is the erase overlay type?
Polygons from an erase layer eliminate an area from the input theme. (overlay and eliminate)
ex. part of cutblock expropriated for parkland.
What is the difference between append and merge?***
- Merge: Combines 2 layers to produce a new combined area
- Append: adds a layer to an existing layer
Spatial Join ***
Creates a new layer containing features from the target layer and attributes from both layers. Based on co-incident space.
ex. plots in polygons.
good for 1:1 or M:1
