Joints/selections/digitizing Flashcards
what are attributes
non spatial data associated with a spatial location
where are attributes stored
in an attribute table
can vector data have numerous attributes attached to one spatial location
YES
what are joints
methods of linking two or more attribute tables
how can two tables be joined together
through a COMMON FIELD
what are relates
a relationship between two or more tables but DOES NOT attach or remove data
what is required for relates
a common field
when are relates preferred over joints
when working with one to many relationships or numerous tables
when is a spatial joint used
when layers DO NOT have a common attribute field
what are join one to one relationships
the joining of information with each feature in a target layer
what are join one to many relationships
multiple join features overlay the target feature = output will have multiple copies of the target feature
what are three types of selections
- interactive selection
- select by attribute
- select by location
when is select by location used
for spatial queries
when is select by attributes used
for database queries
what language do queries use
structured query language
what is a compound query
a query used to make selections based on multiple criteria
what are the logical operators for query
AND
OR
NOT
XOR
contrast the four logical operators
and - selects INTERSECTION between multiple criteria
or - selects everything that meets BOTH criteria (UNION)
not - select what meets the FIRST criteria but NOT the second
Xor - selects all features that ONLY meets the first and second criteria
can the and logical operator be used for the same field
NO
what is a limitation of the AND logical operator
MUST mean both criteria is true
what are spatial queries
selecting features or information based on spatial relationships
what are the different spatial relationships
- intersect
- within a distance
- within
- completely within
- contains
- completely contains
- boundary touches
what is the intersect spatial location
features in the input layer are selected if they completely or partially overlaps with the selecting features
what is the within a distance spatial location
- creates search area from the selecting feature
- selects features that fall WITHIN a certain distance
contrast within and completely within
within
- selects input features that are located COMPLETELY or PARTIALLY within the select feature
completely within
- selects input feature if it DOES NOT share a boundary with selecting feature
contrast contains and completely contains
contains
- selects the input feature that has the selecting feature WITHIN it
completely contains
- selecting feature MUST be completely within the input feature
what is the inverse of within? completely within?
within - contains
completely within - completely contains
what is the boundary touches spatial location
- selects the input if it touches the boundary of the selecting feature
what shapefile must data be to use boundary touches location
lines or polygones
what is digitizing
a process of creating points, lines or polygons which represent features from a map or image
what is important to remember while digitizing
errors propagate during digitizing
what are two types of digitizing
- heads down digitizing
- heads up digitizing
contrast heads up or down digitizing
heads up
- on screen digitizing
heads down
- digitizing tables for hardcopy maps
how does heads down digitizing work
the tablets use a grid of wires to generate a magnetic field which is detected by the cursor
contrast point mode vs stream mode digitizing methods
point
- user identifies the point to be captured by intentionally pressing a button
stream
- points are captured at set time intervals (the user traces over a feature)
what can be an unwanted result of digitizing
sliver polygons
what are sliver polygons
occur when digitized polygons overlay each other and gaps exist between boundaries
