Basic GIS Operations

Question 1

What does GIS data look like?

Answer 1

Location: where you measure something
Attributes: what you measured and its value

Question 2

Layering

Answer 2

Order of the data in presentation

Make sure all layers are in the same projection - does not display data together

Question 3

Buffering

Answer 3

Create a polygon around another point/polygon
Uses straight line distances
Find areas within a user specific distance of points/lines/areas
2 kinds
Dissolved: merge areas together = one area for all buffers together. Tidier
Undissolved: a line for each buffer, overlays etc.

Question 4

Spatial Join (spatial summary0

Answer 4

links different data sets by spatial location
This is different than the table join which uses IDs
For point data to be linked to polygons based on location
Must specific “sum” during the spatial join
No IDs are necessary
Can do polygons into points
Can help answer questions
How many points are within a polygon
How many cases of a disease in an area
input files are 2 shp and the output file is a shp→ attribute table will have all those from original shapefile and the count and or other summary information from join to shapefile
Count: number of the specified shp that are within the boundaries of the starting shp file
\SUM: the sum of attributes in the specific shp (not all will be helpful)

Question 5

Spatial join: nearest

Answer 5

Use to calculate distance nearest a particular point

Need projected data otherwise all outputs in degrees

Question 6

Table Join

Answer 6

one spatial shapefile + nonspatial table
Link with an id file
Headers do not have to match but the info in the columns have to march in table and shp attribute table
It is a temporary link so to make permanent have to export to a new shapefile
Export if a file becomes unstable

Question 7

Clip By

Answer 7

cookie cutter - cutting around a template
Uses the outermost boundary of the shp to delineate what to keep of the shape being clipped
A geo-processing tool

Question 8

Attribute Statistics

Answer 8

: frequency distribution (count, sum etc.)
Add field and calculate
Editing needs to be off before you can use a field calculator
Select before you calculate
Cannot have a zero in the denominator - have to select all non-zero values first

Question 9

Adding X,Y Coordinates to attribute table

Answer 9

Will need to re-add and calculate if re-project from latitude and longitude - won’t automatically convert as ot stored in a shp

Question 10

Adding more spatial data

Answer 10

Adding more spatial data: merge to new dataset DO NOT append to existing
Merge creates a new dataset and keeps original

Question 11

Dissolve by attribute

Answer 11

creates a new coverage by merging adjacent polygons, lines or regions that have the same value for a specified item

Question 12

Basic Operations in ArcToolbox

Answer 12

Simple layering
Spatial join
Buffering
Clip by
Merge
Append to
Dissolve
Intersect
Summarising
calculating