Spatial data management Flashcards
Lecture 12
what is spatial data management?
a group of operations that follow on and is associated with data capturing activities and is used to prepare spatial data for further use.
Refers to the cleaning and fixing of errors in spatial data.
What procedures are included in spatial editing?
Cleaning of captured data by detecting errors and correcting them.
Generalizing through:
* Coordinate thinning and smoothing,
* Aggregating,
* Classifying,
* Recoding and
* Resampling.
What are spatial errors?
can be topological or non-topological errors.
What are topological errors?
Logistical inconsistencies between spatial features
Poorly or ill defined spatial relationships (i.e. nodes/lines/polygons)
Errors that violate topological relationships:
1. Connectivity, or the linking of points or polygons to each other.
2. Adjacency or the sharing of a common boundary of two regions
or polygons.
3. Containment or the inclusion of points/polys in areas
4. Contiguity or the direction that arcs have
What are non-topological errors?
Geometric inaccuracies like missing polygons & distorted lines
Need not be related to spatial relationships
* Variety of basic editing operations that can modify simple
features and create new features from existing features
* Some basic operations are similar to that of topological editing
i.e. Snapping tolerances
* Non-topological editing = spatial editing, BUT no topology gets
defined in the editing process.
What are examples of topological errors?
- Undershoot - lines that don’t meet
- Overshoot – Lines that overshoot connecting node
- Polygons that don’t close
- Polygons that overlap
What is a sliver polygon?
an artifact of digitizing - consequence
pseudo polygon - that doesn’t actually exist.
How to eliminate slivers?
- Poly option: deletes the longest arc and label point of the
selected polygon - Line option: an arc will be merged with its longest neighbor
with which it shares a pseudo node
What ways yo fix non-topological errors includes?
- editing existing features
- creating new features
- edge matching
- generalizations.
Editing existing features
– Extend/trim lines
– Delete/move features
– Reshape features
– Split lines and polygons
non-topological editing creates new features using?
- Buffer: Create boundaries around a feature at an equal
distance in all directions, for example zones of different noise
intensity around an airport - Union: Combine features from different layers into one
- Intersect: Create a new feature from the intersection of
overlapped features in different layers.
How can create New Features by Splitting large data sets into smaller
subsets?
- Clipping portions out
- Sub-setting by feature type or some logical selection criteria
creating new features by?
Union
Interesect
Clip
Split
Merge
Edge matching
Edge-matching is the process to determine which edges (lines) should be linked among candidates. For some cases, one edge will join with only other one and for some other cases, more than two edges will be linked together.
generalizations
Generalizing features through: coordinate thinning, coordinate smoothing, aggregating, classifying, recoding and resampling.
Simplify:
– Line
– Polygon
Smooth:
– Line
– Polygon