Topic 10 Flashcards
(42 cards)
what is isarithmic mapping
deals with continuous fields
elevation mainly
impression of depth
based on the concept of continuity of phenomena
rate of change maps
isometric
isopleth
change of elevation over space = ______
slope
isometric
by far more common
location of points is real
true point data
isopleth
conceptual point data
phenomena we have is continuous, but we measure at a location. measured at the centre of a polygon
where do points come from?
lidar
TIN (triangulated networks) (sketchup angled surfaces)
isolines
rasters (pixels and cells)
Sfm
surveyed points
satellite measurements
how to model continuous surfaces
raster
TIN
isolines
what is thiessen polygon
used for socio-economic data
polygons represent the spacing of the dots themselves
irregular tesallation
what is TIN
triangulated networks
estimating between known points
describe global mapping methods
raster
regression model that produces a surface to then extract elevations
trend surface
shows general trends of the data
extreme values along the edges (nothing to control it if there no points there)
describe local mapping methods
look at the same amount of your point observations to estimate values
Inverse distance weighting
geospatial - kriging
more hyper local/defined
describe inverse distance weighting
estimating values of a point based on nearest neighbours
the closer another point the more influence it has
creates little tragets in your data (data is most likely not dense enough)
geospatial - kriging
often the “best” interpolation method
look at the spatial distribution of points and their attribures and then how it sets up the inverse distance weighting
data distribution controls the search parameters
how to symbolize isarithmic maps
isolines
shading betweeen isolines
continuous tone
fishnet or 3d perspective
augmentation
hillshade
slope, azimuth, curvature
classed values vs. colour ramp
what works better for your map?
hypsometric curve
use of colour and size allocation can be problematic
elevation changes on earths surface
contouring characteristics
contours usually relate to elevation
estimating values
draw line of equal value between data points
inverse weighting distancing
isolines : show lines of equal value
create vector representation of ‘breaks’
can only be ratio or interval measurement level
what are slope and aspect measurements and the two components
slope and aspect are key measurements that can be performed on terrain models
two components
slope (vertical)
aspect (horizontal)
0 = north
90 = east
180 = south
270 = west
slope computations
raster DEM
computation is the ratio of two components
(vertical and window distance)
convert to % by multiplying by 100
can be extended to account for more than 4 neighbours (extended to 8)
complex and used inside ArcGIS
aspect computations
raster DEM
aspect is expressed using angles on a unit circle (circular data)
sign and magnitude of differences reveals the “tilt”
does representation of slope appear less or more noisy (blurry) with larger pixels?
less noisy
small pixels = _____
more noise
usually not as good for slope and aspect maps
precision of slope and aspect maps
derivation of slope and aspect maps from terrain models are very sensitive to precision/accuracy of the input DEM on TIN
questionable
precision is much lower with larger pixels
best is 2x the original data pixel size
deriving slope curvature
measured in slope direction or aspect
spatial change of slope or aspect
spatial derivative
input map
first order produce (slope angle, aspect)
second order products (slope profile, plan curvature, flat, convex, concave)
profile curvature
going down or to 0 (skate ramp) = concave up (+)
becomes steeper (bows out) = convex up (-)
