8. Specifics on Digitizing & Layout tips 1 Week 6 Specifics on Digitizing and More tips on a Layout

8. Specifics on Digitizing & Layout tips

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Week 6

Specifics on Digitizing and More tips on a Layout


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Areas to be covered today

Screen Digitizing of vector data from raster images– See proclibs for steps in adding vectors and

attributes

Defining Shapefiles and Image files


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1. SCREEN DIGITIZING


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ArcMap on-screen Digitizing

A means of translating data usually from an image file into a feature file (data layer)– Initial data appears on the computer screen– Using cursor transform raster to vector

• although can also occur for vector to vector

– Attributes can also be added to new vector file– Good way of abstracting from data set– Good way of getting maps into GIS– Good way of capturing additional information from

an aerial photography or field map

ArcMap on-screen digitizing

Display on-screenUsually from Raster– Could be vector

Transform into vector – data layer use Mouse/cursor draw toolsAttributes possibleExtracting abstracting dataTake visual/spatial data >>transform into>> GIS database

Basic points from which to build your definitionBasic points from which to build your definition


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2. Defining Shapefiles and Image Files in ArcMap


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Imagefile

Imagefiles store raster data but no attributes or entitiesCan be organized/stored in a number of ways depending upon the particular image format.– giff tiff jpeg…

Typically, the image data file contains a header record that stores information about the image -- number of rows and columns in the image, the number of bits per pixel (or raster), the color requirements and the georeferencing information. There are four types of images:– monochrome (one color usually black on white) – pseudocolor (especially when data outside the visible spectrum)– grayscale (shades of black on white) – true color/multiband

(note how similar the definition of Imagefile is to Image Data)


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Shapefile

Shapefiles store feature data (vectors)– Entities– Attributes– Geocodes

Required files– .shp - the file that stores the feature geometry.(points, lines, or

polygons and geocodes) – .shx - the file that stores the index of the feature geometry.– .dbf or excel - the dBASE/Excel file that stores the attribute

information of features. (descriptors)Optional files– A number of optional files also exist, but will not be discussed here

A major difference between Esri shapefiles and image files is the former has attributes attached to entities, the latter has no attributes or entities

Attributes in a .xlsx file


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.shp file in Hex-Dec code for entities


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.shx file – relating entities and attributes, again encoded


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Final Thought

Realize that Screen Digitizing generally creates Shapefiles from Image files (although it is also possible to use it to create a new shapefile from an existing shapefile(s) or other vector formats).

Documents

8. Specifics on Digitizing & Layout tips 1 Week 6 Specifics on Digitizing and More tips on a Layout