Lab 3. DIGITIZING IN ARCMAP

(you might find this link helpfull, too).

3.1 Data

The data for this lab are found in the data folder on the U drive (//Lantang/public/fieldcamp04/data/LAb3). Data include:

• Tif image of geologic map (georiverside.tif)
• DEM
• scanned topographic maps
• a polygon shape layer showing the extent of the mapping area, including the regions each group should digitize.

3.2 Tasks

To complete this lab you will need to do the following (in order):

1) Create shapefiles for:

a) geology (polygons)
c) faults (polylines)
d) structure (points)

2) Populate the shapefiles by digitizing the above features from the geologic map image.

3) For the shapefiles indicated, create the following new attributes fields and fill in their appropriate values:

a) geologic units shapefile:
   1) geologic unit abbreviation;
   2) full unit name;
   3) unit description (I will provide names/abbreviations in lab)

b) faults shapefile: fault type;

c) point shapefile: feature names, dip, strike.

4) Symbolize all shapefiles to resemble the map shown at the end of this lab. 

5) Construct a layout showing the following:

• contour map (100 m intervals only)
• all of the point features you created, labeled
• geologic unit polygons, labeled with unit abbreviations, given below (Unit name,  Abbreviation)
  • modern Alluvium, Qal
  • older Alluvium, Qa
  • Tertiary sandstone, Ts
  • Tertiary rhylotic intrusive, Ti
  • Mesozoic undifferentiated, Mzu
  • McCoy Mountains Formation, Mzm
  • Planet Volcanics, Jp
  • Vampire formation, Jv
  • Eastern Riversides granite, Jg
  • Buckskin formation, Trb
  • Buckskin formation gypsum portion, Trbg
  • Kaibab formation, Pk
  • Coconino quartzite and hermit schist, Pch
  • Supai formation, Ps
  • Redwall marble, Mr
  • Temple butte marble, Dt
  • Muav marble, Cm
  • gneiss and granite, pCgn
• faults, symbolized using a heavier line weight than unit contacts and appropriate tic maks

 

 3.3 Procedure

Create shapefiles in ArcCatalog

• You create a new shape file in ArcCatalog by using the File-New menu. Note that you must already have navigated to a folder in which you have permission to create new files, otherwise when you choose File-New, there will be no options for shapefile.

  When you choose File-New, you must specify a new shapefile name and feature type (point, line, or polygon).

• You should also specify a coordinate system by pressing the Edit button. The coordinate system of the shapefile should be the same as the rectified image. Can you tell what projection the .tif image is in?

• Add the new shapefiles and the rectified image to a new map document.

3.4 Digitizing features

Some general strategies for digitizing:

• Start the polygon layer with the Task = "Create New Feature", after having first digitized the map boundary into a separate shapefile so that it can be used for snapping.
• Nearly all other geo. polygons can be most easily created by appended to the first one by using the Task = "Auto Complete Polygon".  Those that cannot are island polygons; save them until last.
• Digitize from one edge of the map to the other
• If you find yourself repeating an existing polygon boundary, you've started in the wrong place - start again somewhere else on the same polygon and think through how you can Auto Complete without repeating that segment.
• Examine the map carefully and try to think a few steps ahead.
• Use the new layer's attribute table as you work - keep it open and use it to select polygons when you've forgotten what you've already completed.  After saving your edits, close and reopen the attribute table - a bug in the software does not allow it to update properly.

 1. General digitizing procedure:
   a) Turn on Editing toolbar, Start Editing;
   b) On the toolbar set Target to the file you will digitize into;
   c) Set Snapping (under the Edit menu on the Editing toolbar)
   d) Choose Task – “Create New Feature” – on toolbar;
   e) Select Tool – Pencil (for other tools see Help files) on toolbar;
   f) Begin outlining feature – create a “Sketch” - Click to create a vertex; create as needed to outline feature. Put additional vertices at every point where boundaries of map features intersect (a geologic unit boundary, for example) – you will need these later. Additional vertices can be created as you trace or after the sketch is complete;
   g) Finishing feature outline with double click;
   h) SAVE EDITS (editing toolbar menu), stop editing.

2. To digitize adjacent polygons:

a) Change Task to “Auto Complete Polygon”
b) Open Snapping window (under Editing menu). Check boxes adjacent to "vertices" for the layer you are digitizing; leave all others unchecked for now. In the snapping window, order the layers by dragging and dropping so that the layer you are digitizing is at the top of the list – this sets snapping to this layer at the highest priority
c) Set Task to “Auto Complete Polygon”
d) Begin at any vertex of previous polygon
e) Trace outline, adding vertices as needed
f) Double click on vertex of adjacent polygon to finish:

1) If no vertex exists at ending spot, end at the nearest vertex, then delete the sketch you’ve made;
2) Change Task to “Modify Feature”; check that the target still set to the file you want;
3) Use the “Arrowhead” tool next to the pencil and select the polygon to which you need to add a vertex – this should cause the polygon to be outlined and to show green vertices;
4) With the Arrowhead tool still operative, right-click on the polygon boundary where you want to add a vertex and “Add vertex”.
5) Change Task back to Auto Complete Polygon and start again 4)

3. To split a polygon:

a) Set Task to “Cut Polygon Features”
b) Use the “Arrowhead” tool next to the pencil in the Editor toolbar to select the polygon to split.
c) Use the pencil tool to draw the cut line across the polygon. Double click to end the line and clip the polygon.
d) SAVE EDITS

 4. To digitize “island polygons” – polygon surrounded by another polygon:

a) Set Task to “Create New Feature”
b) Digitize the island, double clicking to finish
c) With new island poly. still selected, under Editor menu, select “Clip” to clip a hole in the polygon(s) beneath
d) SAVE EDITS
e) check with the Info tool to see if more than one polygon exists at the site of the island - this may or may not be necessary; island polygons are sometimes created automatically when you draw a polygon on top of another one, sometimes not.

5. To include an island polygon as part of another feature (to create a “multipart feature”):

a) While in the editing mode, with the proper Target selected, use the “Arrowhead” tool to select both features, or select both within the attribute table;
b) From the Editor drop-down menu, select Merge;
c) This will combine the features into one multipart feature that comprises a single record in the attribute table.

6. To remove an island polygon or split up any multipart feature:

a) select the feature;
b) right-click on the feature and choose “Properties”;
c) highlight the part you wish to delete in the left hand side of the properties table;
d) hit the keyboard delete key

 For more help with digitizing, send me(akciz@mit.edu) or Daniel (dsheehan@mit.edu).

3.5 Adding a field to an attribute table and populating it with values

• Open Attribute Table – add a new field (If an editing session is running, Save your edits if needed, and Stop editing before adding a new field.).
  • Type=text; 12 characters or more if needed to store feature names or ID. Leave attribute table open for editing.
  • Start editing. Type feature attribute into attribute table for the feature just digitized.
  • Save edits, and Stop editing when done.

3.6 Symbolize and label on the basis of the relevant attributes you created.