Spatial analysis with geographical information system (GIS) Geographic information system

1 spatial analysis geographical information system (gis)

1.1 slope , aspect
1.2 data analysis
1.3 topological modeling
1.4 geometric networks
1.5 hydrological modeling
1.6 cartographic modeling
1.7 map overlay
1.8 geostatistics
1.9 address geocoding
1.10 reverse geocoding
1.11 multi-criteria decision analysis
1.12 data output , cartography
1.13 graphic display techniques
1.14 spatial etl
1.15 gis data mining

spatial analysis geographical information system (gis)

gis spatial analysis rapidly changing field, , gis packages increasingly including analytical tools standard built-in facilities, optional toolsets, add-ins or analysts . in many instances these provided original software suppliers (commercial vendors or collaborative non commercial development teams), while in other cases facilities have been developed , provided third parties. furthermore, many products offer software development kits (sdks), programming languages , language support, scripting facilities and/or special interfaces developing 1 s own analytical tools or variants. website geospatial analysis , associated book/ebook attempt provide reasonably comprehensive guide subject. increased availability has created new dimension business intelligence termed spatial intelligence which, when openly delivered via intranet, democratizes access geographic , social network data. geospatial intelligence, based on gis spatial analysis, has become key element security. gis whole can described conversion vectorial representation or other digitisation process.

slope , aspect

slope can defined steepness or gradient of unit of terrain, measured angle in degrees or percentage. aspect can defined direction in unit of terrain faces. aspect expressed in degrees north. slope, aspect, , surface curvature in terrain analysis derived neighborhood operations using elevation values of cell s adjacent neighbours. slope function of resolution, , spatial resolution used calculate slope , aspect should specified. various authors have compared techniques calculating slope , aspect.

the following method can used derive slope , aspect:

the elevation @ point or unit of terrain have perpendicular tangents (slope) passing through point, in east-west , north-south direction. these 2 tangents give 2 components, ∂z/∂x , ∂z/∂y, used determine overall direction of slope, , aspect of slope. gradient defined vector quantity components equal partial derivatives of surface in x , y directions.

the calculation of overall 3x3 grid slope s , aspect methods determine east-west , north-south component use following formulas respectively:

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=




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{\displaystyle \tan s={\sqrt {\left({\frac {\partial z}{\partial x}}\right)^{2}+\left({\frac {\partial z}{\partial y}}\right)^{2}}}}

tan
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a
=

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−
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{\displaystyle \tan a=\left({\frac {\left({\frac {-\partial z}{\partial y}}\right)}{\left({\frac {\partial z}{\partial x}}\right)}}\right)}

zhou , liu describe formula calculating aspect, follows:

a
=

270

∘


+
arctan
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−

90

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{\displaystyle a=270^{\circ }+\arctan \left({\frac {\left({\frac {\partial z}{\partial x}}\right)}{\left({\frac {\partial z}{\partial y}}\right)}}\right)-90^{\circ }\left({\frac {\left({\frac {\partial z}{\partial y}}\right)}{\left|{\frac {\partial z}{\partial y}}\right|}}\right)}

data analysis

it difficult relate wetlands maps rainfall amounts recorded @ different points such airports, television stations, , schools. gis, however, can used depict two- , three-dimensional characteristics of earth s surface, subsurface, , atmosphere information points. example, gis can generate map isopleth or contour lines indicate differing amounts of rainfall. such map can thought of rainfall contour map. many sophisticated methods can estimate characteristics of surfaces limited number of point measurements. two-dimensional contour map created surface modeling of rainfall point measurements may overlaid , analyzed other map in gis covering same area. gis derived map can provide additional information - such viability of water power potential renewable energy source. similarly, gis can used compare other renewable energy resources find best geographic potential region.

additionally, series of three-dimensional points, or digital elevation model, isopleth lines representing elevation contours can generated, along slope analysis, shaded relief, , other elevation products. watersheds can defined given reach, computing of areas contiguous , uphill given point of interest. similarly, expected thalweg of surface water want travel in intermittent , permanent streams can computed elevation data in gis.

topological modeling

a gis can recognize , analyze spatial relationships exist within digitally stored spatial data. these topological relationships allow complex spatial modelling , analysis performed. topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), , proximity (how close something else).

geometric networks

geometric networks linear networks of objects can used represent interconnected features, , perform special spatial analysis on them. geometric network composed of edges, connected @ junction points, similar graphs in mathematics , computer science. graphs, networks can have weight , flow assigned edges, can used represent various interconnected features more accurately. geometric networks used model road networks , public utility networks, such electric, gas, , water networks. network modeling commonly employed in transportation planning, hydrology modeling, , infrastructure modeling.

hydrological modeling

gis hydrological models can provide spatial element other hydrological models lack, analysis of variables such slope, aspect , watershed or catchment area. terrain analysis fundamental hydrology, since water flows down slope. basic terrain analysis of digital elevation model (dem) involves calculation of slope , aspect, dems useful hydrological analysis. slope , aspect can used determine direction of surface runoff, , hence flow accumulation formation of streams, rivers , lakes. areas of divergent flow can give clear indication of boundaries of catchment. once flow direction , accumulation matrix has been created, queries can performed show contributing or dispersal areas @ point. more detail can added model, such terrain roughness, vegetation types , soil types, can influence infiltration , evapotranspiration rates, , hence influencing surface flow. 1 of main uses of hydrological modeling in environmental contamination research.

cartographic modeling

an example of use of layers in gis application. in example, forest-cover layer (light green) forms bottom layer, topographic layer (contour lines) on it. next standing water layer (pond, lake) , flowing water layer (stream, river), followed boundary layer , road layer on top. order important in order display final result. note ponds, layered under streams, stream line can seen overlying 1 of ponds.

dana tomlin coined term cartographic modeling in phd dissertation (1983); later used in title of book, geographic information systems , cartographic modeling (1990). cartographic modeling refers process several thematic layers of same area produced, processed, , analyzed. tomlin used raster layers, overlay method (see below) can used more generally. operations on map layers can combined algorithms, , simulation or optimization models.

map overlay

the combination of several spatial datasets (points, lines, or polygons) creates new output vector dataset, visually similar stacking several maps of same region. these overlays similar mathematical venn diagram overlays. union overlay combines geographic features , attribute tables of both inputs single new output. intersect overlay defines area both inputs overlap , retains set of attribute fields each. symmetric difference overlay defines output area includes total area of both inputs except overlapping area.

data extraction gis process similar vector overlay, though can used in either vector or raster data analysis. rather combining properties , features of both datasets, data extraction involves using clip or mask extract features of 1 data set fall within spatial extent of dataset.

in raster data analysis, overlay of datasets accomplished through process known local operation on multiple rasters or map algebra , through function combines values of each raster s matrix. function may weigh inputs more others through use of index model reflects influence of various factors upon geographic phenomenon.

geostatistics

geostatistics branch of statistics deals field data, spatial data continuous index. provides methods model spatial correlation, , predict values @ arbitrary locations (interpolation).

when phenomena measured, observation methods dictate accuracy of subsequent analysis. due nature of data (e.g. traffic patterns in urban environment; weather patterns on pacific ocean), constant or dynamic degree of precision lost in measurement. loss of precision determined scale , distribution of data collection.

to determine statistical relevance of analysis, average determined points (gradients) outside of immediate measurement can included determine predicted behavior. due limitations of applied statistic , data collection methods, , interpolation required predict behavior of particles, points, , locations not directly measurable.

hillshade model derived digital elevation model of valestra area in northern apennines (italy)

interpolation process surface created, raster dataset, through input of data collected @ number of sample points. there several forms of interpolation, each treats data differently, depending on properties of data set. in comparing interpolation methods, first consideration should whether or not source data change (exact or approximate). next whether method subjective, human interpretation, or objective. there nature of transitions between points: abrupt or gradual. finally, there whether method global (it uses entire data set form model), or local algorithm repeated small section of terrain.

interpolation justified measurement because of spatial autocorrelation principle recognizes data collected @ position have great similarity to, or influence of locations within immediate vicinity.

digital elevation models, triangulated irregular networks, edge-finding algorithms, thiessen polygons, fourier analysis, (weighted) moving averages, inverse distance weighting, kriging, spline, , trend surface analysis mathematical methods produce interpolative data.

address geocoding

geocoding interpolating spatial locations (x,y coordinates) street addresses or other spatially referenced data such zip codes, parcel lots , address locations. reference theme required geocode individual addresses, such road centerline file address ranges. individual address locations have historically been interpolated, or estimated, examining address ranges along road segment. these provided in form of table or database. software place dot approximately address belongs along segment of centerline. example, address point of 500 @ midpoint of line segment starts address 1 , ends address 1,000. geocoding can applied against actual parcel data, typically municipal tax maps. in case, result of geocoding positioned space opposed interpolated point. approach being increasingly used provide more precise location information.

reverse geocoding

reverse geocoding process of returning estimated street address number relates given coordinate. example, user can click on road centerline theme (thus providing coordinate) , have information returned reflects estimated house number. house number interpolated range assigned road segment. if user clicks @ midpoint of segment starts address 1 , ends with 100, returned value somewhere near 50. note reverse geocoding not return actual addresses, estimates of should there based on predetermined range.

multi-criteria decision analysis

coupled gis, multi-criteria decision analysis methods support decision-makers in analysing set of alternative spatial solutions, such ecological habitat restoration, against multiple criteria, such vegetation cover or roads. mcda uses decision rules aggregate criteria, allows alternative solutions ranked or prioritised. gis mcda may reduce costs , time involved in identifying potential restoration sites.

data output , cartography

cartography design , production of maps, or visual representations of spatial data. vast majority of modern cartography done of computers, using gis production of quality cartography achieved importing layers design program refine it. gis software gives user substantial control on appearance of data.

cartographic work serves 2 major functions:

first, produces graphics on screen or on paper convey results of analysis people make decisions resources. wall maps , other graphics can generated, allowing viewer visualize , thereby understand results of analyses or simulations of potential events. web map servers facilitate distribution of generated maps through web browsers using various implementations of web-based application programming interfaces (ajax, java, flash, etc.).

second, other database information can generated further analysis or use. example list of addresses within one mile (1.6 km) of toxic spill.

graphic display techniques

traditional maps abstractions of real world, sampling of important elements portrayed on sheet of paper symbols represent physical objects. people use maps must interpret these symbols. topographic maps show shape of land surface contour lines or shaded relief.

today, graphic display techniques such shading based on altitude in gis can make relationships among map elements visible, heightening 1 s ability extract , analyze information. example, 2 types of data combined in gis produce perspective view of portion of san mateo county, california.

the digital elevation model, consisting of surface elevations recorded on 30-meter horizontal grid, shows high elevations white , low elevation black.
the accompanying landsat thematic mapper image shows false-color infrared image looking down @ same area in 30-meter pixels, or picture elements, same coordinate points, pixel by pixel, elevation information.

a gis used register , combine 2 images render three-dimensional perspective view looking down san andreas fault, using thematic mapper image pixels, shaded using elevation of landforms. gis display depends on viewing point of observer , time of day of display, render shadows created sun s rays @ latitude, longitude, , time of day.

an archeochrome new way of displaying spatial data. thematic on 3d map applied specific building or part of building. suited visual display of heat-loss data.

spatial etl

spatial etl tools provide data processing functionality of traditional extract, transform, load (etl) software, primary focus on ability manage spatial data. provide gis users ability translate data between different standards , proprietary formats, whilst geometrically transforming data en route. these tools can come in form of add-ins existing wider-purpose software such spreadsheets.

gis data mining

gis or spatial data mining application of data mining methods spatial data. data mining, partially automated search hidden patterns in large databases, offers great potential benefits applied gis-based decision making. typical applications include environmental monitoring. characteristic of such applications spatial correlation between data measurements require use of specialized algorithms more efficient data analysis.