1. 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

2. 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

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

4. 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

5. 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

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

7. 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. 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

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

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

11. 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

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

13. 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

14. 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

15. 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