Gis Tutorial Purnawan

3. Raster and Vector GIS measurement

Question 3a Raster Gis Distance measurement

C = [3x300]²+[7x100]²

Euclidian

Manhattan

M = 3 X 300 + 7 X 100 = 1600 m

CC

Source : Google Maps

= 1140.17 m

3b. Vector GIS Area measurement

A

B

F

C

D

E

600 m


Formulation

• Area of rectangular Area = Length x Width

• Area of triangularArea = ½ Length x Width

What total Area of Caird Park ?

Area A and B

• Area A = 550 x 375 206250 m²

• Area B = 1100 x 300 330000 m²


Area C, D and E

• Area C = ½ 550 x 600 175000 m²

• Area D = ½ 300 x 50 7500 m²• Area E = ½ 250 x 50 6250 m²


Area F• Area F = ½ 1050 x 250 131250 m²


• Area A = 206250 m²• Area B = 330000 m²• Area C = 175000 m² • Area D = 7500 m²• Area E = 6250 m²• Area F = 131250 m²

• Total = 846250 m² Approx True ????

So what is wrong ?

Area C = 165000 m²

4. Six Key elements of map design ?

• Frame Of Reference• Projection Used• Feature to be Mapped• Level Of generalization• Annotation• Symbolism

1 5 7

N

m

Question ?

•How far does the car move ?•Where does it move ?

Question :

The Frame reference

Heywood, et.al, An Introduction to GIS, p255

What are the 6 key maps design elements

Frame Reference

• A map is scale model of the real world so it needs some form of spatial reference so the user can fix its location in the real world. Mechanism that can be used to provide this:– A grid with lines (representing latitude

longitude) or planar (x.y) co-ordinates– A north arrow in conjunction with a scale bar– An inset map


Projection Used

• Map projections can radically affect measurements such as area or distance. Small scale maps of larger areas are more affected by the projection method. For maps of large areas, decision need to be made regarding what is most important (i.e. area, distance, directions, lines of true scale etc)


Question


Projection


Features to be mapped

• Maps are by definition a communication device for spatial information, so it is important that

the map shows only what is necessary to get that intended message. It should contain no distractions



Level of generalisation• Balance of detail is critical. Too much –

map is difficult to read, too little – map may be missing vital information.Deciding what to ‘leave in’ or ‘leave out’ is a difficult choice. (For example, in designing a road map – which smaller roads would you leave out? This would depend greatly on why you

are mapping the roads... What makes an individual road more or less significant

than another? In all depends on context. Source : Google Maps


Annotation

• Annotation is textual and graphical information that labels the maps, details the features or provides supplementary information.It should be appropriate and economic.Examples of annotation: numerical guides, frame of reference (also a form of annotation), map title, legend.

Question


Annotation


SymbolismSymbols used on the map to

represent the real world. Symbols on a map are either, points, lines or areas. Shape and pattern of symbols should also bear some relation to the feature being represented. Whatever symbols are

decided upon, a ‘legend’ or ‘key’ must be provided so the users understand what they are looking at.Colours are also important. They should where possible match the real world i.e. Rivers should be blue, forests - green so as not to confuse users. If you coloured a river black, users may think it’s a road

http://www.simmons.edu/i/maps/mapOverviewDetails.png

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