chap 5, 8 Flashcards
5km cest combien en metre
5000m
5cm cest combien en km
500,000km
Exercise: If the graphic scale shows by measurement
that 2 cm represents 5 km, what is the RF of your map?
The RF is 1:250,000
Exercise: You have a map with a RF of 1:75,000 and
you want to draw a graphic scale representing 1 km
on it. How long should be your graphic scale in cm?
1.33 cm on your map would represent 1 km on the
ground
map projection
transforming the curve surface to a flat surface
mercator map projection
preserve shape, changes areas
equal-area map projection
preserve area, distorts shape (gall-peter projection)
Mollweide projection
minimiza shape distortions of regions of greatest interest
peters (gall-peters) projection
qual-area map, but shape not conserved, cylindrical equal-area projection, highlight the importance of the size of southern continent
the geographic coordinate system (GIS)
preserves nothing but distance
the van der grinten projection
does not preserve shape or area, but minimizes their distortions in all but polar regions
robinson projection
preserves neither area nor shape, but reduces the distortion of both
small scale
large area, more generalization, more classification
large scale
smaller area, more details
universal transverse mercator (UTM)
divided into 60 zones, each 6 degree wide
state plane coordinate system (SPCS)
used only in the united states, which is divided into over a hundred areas
geoid
more irregular than the ellipsoids but smoother than Earth’s physical surface
Graticule
imaginary network of parallels and meridians
two Coordinate systems
non-projection coordinate system and projected coordinate system
non-projected coordinate system
geographic coordinate; based on lat/long which correspond to angles at the center of the earth based on an origin and on an ellipsoid
serve for; locating precisely each earth feature
representing the earth (3D) on a map (2D)
preserves distance, but does not preserve shape or area
projected coordinate system
the mathematical transformation applied to convert a spherical coordinate system to a planar coordinate system
different types of projections based on
source of projection
projection surface
flat plane
conic
cylindrical
center of projection; contact between projection surface and ellipsoid projected (point or line)
Polar (center on a pole)
Equatorial (center on the equator)
Transverse (center to a line at 90° to this earth’s polar axis (parallel to equator)
Oblique: center on a non-specific point/line
projection preserve either
shape
area
distance/direction
most of everything
multiple media to show your map
computer monitor
black and white, on paper
color, on paper
projected
posters
document
goal of the map; source of data; types of data; design decision; intermediary versions
evaluate
does the map achieve its goal?; on-going challenge of the map; ask for external perspectives
review
who has the final say on your map should review it before making it public
why do we need scale, generalization and projection
the earth is a huge sphere
a map is a small flat plane
we need to depict this huge sphere on a small flat plane
scale and generalization deal with the size transformation
projection deals with the shape transformation
scale
map scale is the ratio between a distance on the map and the corresponding distance on the earth, with the distance on the map always expressed as one
scale is used for
measuring distance between features
assessing the surface covered by a map
evaluating the size of the area mapped
keeping constant spatial relationships between features
scale; numerical
representative fraction; 1:50,000
scale; verbal statement
ex. one centimeter represents one kilometer
scale; graphic/visual
bar scale
RF
divide the earth scale by the map scale
selection
are all the features selected necessary?
dimension change
are all the dimensions appropriate to show the level of details
simplification
how simplified can a feature be and still be recognized
smoothing
how much can you smooth a fissure without losing its character
displacement
are important map features interfering with one others
enhancement
make it more accurate (intensification)
unclassified scheme
unique visual shade to every unique data value
quantile scheme
place the same number of data values in each class (but can place very different values in the same class)
Equal-Interval Scheme
places boundaries between classes at regular (equal) intervals
Natural-Breaks Scheme
minimize differences between values within classes and maximize differences between values in different classes (ex. makes poverty seem more significant)
Unique Scheme
class boundaries can be set by external criteria (ex. a gov. program offers special funds to counties with over 25% poverty, a two-class map shows which counties qualify and which don’t)
scale reduction
adapt the map at different scales
constant scale
enhance the point of the map
