intro to GIS Flashcards
GIS software
ArcGIS
QGIS
GEOMEDIA- local gvts
Smallworld (GE)-used by utility companies
spatial features can be
discrete or continuous
discrete spatial features
houses, roads, wells = vector
continuous spatial features
rainfall, elevation = raster
discrete geographic features are better represented by
georelational vector data model (points, lines and polygons)
vector data rules
- thematic object forms its own layer ( roads separated from railways)
each layer can have only one type of feature ( can’t mix points with polygons)
continuous geographic features are better represented by
raster data model or grids & cells
an example of raster data model : the digital elevation model (DEM)
a digital terrain representation technique, where elevation values/topography are stored in raster cells
- useful for hydrological modeling
forms of raster data models
- aerial photographs (digital orthophoto quadrangle)
- satellite images
remote sensing and GIS
a form of ‘primary’ data collection
- can be used to collect information about objects on the ground using satellite or plane based sensors
pixel values in a raster image
valued between 0-255
0 - black
255- bright cell
colors are a proxy for the number values because
different land covers reflect different colors
why vegetation reflects near infrared
absorb red, green, and blue, to convert into food
infrared is all that’s left
spatial analysis in GIS
map projections
attribute data
cartography: making a map & choropleth maps
vector analysis with GIS using
buffers
overlays
-union
-clip
-intersection