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

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 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips 1. SCREEN DIGITIZING 8. Specifics on Digitizing & Layout tips

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 8. Specifics on Digitizing & Layout tips

ArcMap on-screen digitizing Basic points from which to build your definition Display on-screen Usually from Raster Could be vector Transform into vector – data layer use Mouse/cursor draw tools Attributes possible Extracting abstracting data Take visual/spatial data >>transform into>> GIS database

2. Defining Shapefiles and Image Files in ArcMap 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips Imagefile Imagefiles store raster data but no attributes or entities Can 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 (geocodes). 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) 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips 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 8. Specifics on Digitizing & Layout tips

Attributes in a .xlsx file 8. Specifics on Digitizing & Layout tips

.shp file in Hex-Dec code for entities 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips .shp file Stores type of Entity (point line of polygon) Enables the drawing of the Entity into geographic space (links to Geocodes) 8. Specifics on Digitizing & Layout tips

.shx file – relating entities and attributes, again encoded 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips .shx file Fancy word – enables a Relational Database Basically each Entity has an ID number And each line in the Attribute table has the same ID .shx “relates” these two pieces together based on the ID 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips Metaphor .shx is like a “secretary” that finds an entity in the .shp file and “draws” it And then looks at the .dbf file for an attribute linked (same ID) to the entity, and “colors” or represents it appropriately 8. Specifics on Digitizing & Layout tips

8. Specifics on Digitizing & Layout tips 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). 8. Specifics on Digitizing & Layout tips