How does satelite imaging work
- uses energy from sun
- interacts with earths surface
- travels to satellite sensor
- transmitted to receiving station
Digital Capture (how do you input data into GIS)
-Keyboard Entry attribute data - entered in tables spatial data - rarely done -Digitize User Link data from paper or screen is digitized (traced) in a series of points -Scan User Link scan to generate raster image georeference
What is digitizing?
what are the two modes?
Converting paper to digital information.
- Point mode
- Stream mode
What is an important part of digitizing with regards to data quality?
what is drafting assist?
Data must be perfect for accurate results
- Drafting assist is a computer assisted method of perfecting data
What is an important feature of GIS data with regards to how data is displayed?
All data is displayed as a series of points. Even lines are just a series of points.
What is scanning?
Computer “photocopying” of data to generate a raster image, vectorize the data (optional), and georeference it.
What is an “artifact”?
an artifact is a data error that generates a spike or a loop in what should be a straight line.
What are some user generated errors?
- poor tracing
- sliver polygons (overlapping polygons)
- under/overshoots (not quite matching node ex, road too short or long)
- missing or duplicate features (accidentally missing points or duplicating points when tracing.
- not updating database
What is a major advantage of GIS over paper maps?
GIS has the ability to create overlays and compare data easily.
What are 4 important things to remember when combining data (data transformations)?
- Convert to same projection
- Convert to same datum
- Edge matching adjacent maps
- Rubber sheeting
What is rubber sheeting?
When maps are overlayed, incoming map is stretched to match base map. ( based on control points. )
What generalizations are made in GIS to improve visual quality of maps?
- Line smoothing of roads and streams
- weeding coordinates ( reduce number of coordinates for a smaller database and faster operation )
What is the purpose of a map?
- navigation
- communication (feature location, size, amount, pattern)
- used to conduct spatial analysis for decision making.
What are the key points of cartographic design?
- Concept before compilation (purpose and audience)
- Hierarchy with harmony (exaggerate important information on map)
critical map elements: figure
background map data: ground - Simplicity from sacrifice
selection (how many map layers do you want to show?)
simplification/aggregation
only show relevant info - Max info at minimal cost
(5-7 classes max) - Engage emotion
What are important map making “Do’s” ? (6)
- use a few related colors
- use a few font types (vary size, boldness)
- use stronger colors for important features
- use subdued colors for background
- keep balance and symmetry
- clean and simple (avoid clutter and unnecessary detail)
What is a cartogram?
spatial data is stretched to match the value of the target attribute for the map.
Main difference between projections and datum?
Datum: uses an ellipsoid to reference the earths surface
Projection: transfer features from the globe onto flat maps (distorts data in different ways depending on the shape of the projection.)
What are the GIS data sources?
-GIS Map Data Base maps (GeoBC Topo) Thematic maps (forest cover, watershed etc) -Remote Sensing Lidar Satellite Orthophoto -Field Surveys GPS Survey file (RoadEng)
What does COGO stand for?
Coordinate Geometry (entering coordinates by hand)
