Spatial Data Formats

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Spatial Data Formats. Need data for a GIS?. Just photograph a topographic map Better yet, download one from the internet But are the roads, buildings, and other “objects” on this photo GIS layers?. Stages of development:. - PowerPoint PPT Presentation

Transcript of Spatial Data Formats

Spatial Data Models

CS 128/ES 228 - Lecture 4b3Stages of development:Conceptual model: select the features of reality to be modeled and decide what entities will represent them

Spatial data model: select a format that will represent the model entities

Spatial data structure: decide how to code the entities in the models data filesCS 128/ES 228 - Lecture 4b42. Spatial data modelsRaster



and attribute data

Spatial data formats:

Fig. 3.1 in 3rd ed.CS 128/ES 228 - Lecture 4b5Raster formatFeatures represented by cell contents

Spatial precision limited by cell size

Surfaces modeled as continuous values (almost)

Fig. 3.9 in 3rd ed.CS 128/ES 228 - Lecture 4b6Vector formatDiscrete features explicitly represented

Spatial precision limited by number format

Surfaces shown by contours rather than continuous values

Fig. 3.9 in 3rd ed.CS 128/ES 228 - Lecture 4b7Object-oriented formatsLeave details for CS majors

Fig. 4.17 in 3rd ed.CS 128/ES 228 - Lecture 4b8Thematic data (a.k.a. attribute data)Quantitative or descriptive

May represent 1 or many themes

Tied to a spatial reference

Represented differently in raster vs. vector formatsCS 128/ES 228 - Lecture 4b9Scales of measurementDataUnitScaleResort nametextNominalResort rankingvalueOrdinalWinter temp.oCIntervalSize of ski aream2RatioHeywood et. al. 2006 Table 2.1CS 128/ES 228 - Lecture 4b10Spatial modeling in raster formatBasic entity is the cell

Region represented by a tiling of cells

Cell size = resolution

Attribute data linked to individual cells

CS 128/ES 228 - Lecture 4b11Attribute data in raster formatAttribute data are used to create symbology for each cell

CS 128/ES 228 - Lecture 4b12Additional attribute dataSome GISs provide a VAT linked to individual cells (e.g. ArcInfo GRID)

VAT data then accessible to database management system

Unlimited additional fields CS 128/ES 228 - Lecture 4b13Attribute data for a vector layerEach entity is linked to a row in an attribute table

Themes not (usually) displayed but available via Identify tool

CS 128/ES 228 - Lecture 4a14Vectors are good at modeling roadways or wiring consist of discrete components; types and order of the connections are key

Spaces between the network components generally not of interestBottom : networks

CS 128/ES 228 - Lecture 4a15Rasters are good at modeling they model a continuous feature as a 2- or 3-D layer

every location has a value, even if only interpolated from discrete samples

Both: surfacesCS 128/ES 228 - Lecture 4a16Topographic maps use contoursbut the elevation between contour lines is undefined

CS 128/ES 228 - Lecture 4a17Digital terrain models

Every cell has an elevation valueFig. 3.32 in 3rd ed.CS 128/ES 228 - Lecture 4a18Precision agriculture

Aerial photographSoil pH Crop yieldCS 128/ES 228 - Lecture 4a19OceanographyEstimate of phytoplankton distribution in the surface ocean: global composite image of surface chlorophyll a concentration (mg m-3) estimated from SeaWiFS data (Source: NASA Goddard Space Flight Center, Maryland, USA and ORBIMAGE, Virginia, USA).

CS 128/ES 228 - Lecture 4b20Rasters are a type of TesselationA closed shape or polygon that repeats on all sides without any gaps or overlaps

Three regular polygons tesselate the plane:SquareEquilateral triangle Hexagon

CS 128/ES 228 - Lecture 4b21TilingsIn 1922 Escher visited the Alhambra palace and saw the wall tilings of the Moors. He was excited to find other artists who had been captivated by tilings, but also made this revealing comment: "What a pity their religion forbade them to make graven images."

CS 128/ES 228 - Lecture 4b22Eschers tesselations

CS 128/ES 228 - Lecture 4b23Quilters also tesselate

Designing Tesselations by Jinny BeyerCS 128/ES 228 - Lecture 4b24Effects of resolution rasterLarger cells:less precise spatial fix

line + boundary thickening

features too close overlap - less detail possible

Fig. 3.10 in 3rd ed.CS 128/ES 228 - Lecture 4b25Advantages of raster formatmany data sets available

easy to overlay multiple themes

able to represent multiple continuous surfacesdifferent file formats readily inter-converted

fast computer lookup and displayCS 128/ES 228 - Lecture 4b26Limitations of raster formatpoor representation of discrete objects

exact boundary location difficult

constant resolution throughout the region modeled

generates very large data sets

difficult to change projection or coordinate system

CS 128/ES 228 - Lecture 4b27Raster layers dont share well

CS 128/ES 228 - Lecture 4b28Raster layers are normally projected

Note the datum and projection/ coordinate system

Special software needed to re-projectCS 128/ES 228 - Lecture 4b29Summary: Raster formatHuge amounts of spatial data are available in raster format

Rasters are the format of choice for continuous features

Rasters do a poor job of representing discrete features