GIS In Archaeology

GIS In Archaeology

Lab Exercise 7

Step 1: Modify Hillshade Parameters
In the last exercise we created a hillshade map from the DEM.BILdataset. At the Hillshade parameters window we accepted the defaultvalues (Azimuth: 315; Altitude: 45; Z Factor: 1). The procedure createda somewhat muted looking pseudo 3-D view of the terrain. It is possibleto exaggerate the elevation differences in order to create a moredramatic hillshade model.
Rerun a hillshade analysis for the DEM.BIL raster layer but this timeat the parameters window specify a Z Factor: of 5. The hillshade layercreated by these parameters exaggerates the differences in elevation(the Z-values) and produces a more accentuates the terrain hillshadingmodel.
The Azimuth parameter refers to the angle at which the hypothetical sunis sitting in relationship to the terrain (0 = North, 90 = East, 180 =South, 270 = West). The default setting of 315 places the ‘sun’ sourceto the northwest of the DEM.
The altitude parameter refers to the height of the sun, but it isexpressed in terms of the suns angle in relationship to the ground. Analtitude value of 0 places the sun level with the terrain (ie on thehorizon), an altitude value of 90 models the sun as though it isdirectly overhead.
Try playing with various parameter values to see the effects and understand how these parameters interact with one another.

Step 2: Raster Scales Effects on Raster Summaries
In the last exercise we used the Spatial Analyst to create a slopelayer from the DEM and a distance to Water layer based on the Riverslayer. The model that we were using was that all other things beingequal when select a location for a settlement, humans will tend tofavor flatter lands over steeper lands and land closer to water overland further from a water source. In order to combine these twovariables (slope and distance to water) we used the Raster Calculatorto add the two values together.
The idea was to create a summary layer that would combine both theeffect of both these variables on human settlement decisions. However,if we examine the resulting map in comparison to the distance to watermap we can see that they are extremely similar. This is because thevalues for distance to water range from 0 to 10,000 whereas slopevalues only range from 0 to 57.4. This means that the effect of thedistance to water layer swamps out the impact of the slope variable. Weneed to put the slope and distance to water variables onto a similarscale so that neither one dominates the combination

Step 3: Reclassify Slope Values
A brief analysis of sites in the region indicates that in general aslope of 0 to 7.5 degrees has no appreciable negative impact on humansettlement decisions (these are basically flat lands). Slopes of 7.5 to15 degrees have a slight negative impact and slopes over 15 degreesseem to generally have been considered to be too steep for habitation.We will reclassify the lands based on the following table:
Slope Slope Class Slope Class Label
0 – 7.5% 1 Flat (under 7.5%)
7.5 – 15% 2 Moderate (7.5-15%)
15 – 60% 3 Steep (over 15%)

Clickthe down arrow next to the Spatial Analyst entry in the Spatial AnalystToolbox. Select Reclassify from the drop down menu. Make sure that theInput Raster is the slope layer. The Reclassify window will convert thecurrent value ranges under the Old values column to be the values inthe New values column. Currently there are entries under Old values butwe only need 3 and we need to set our own ranges. Highlight the 2nd rowin the reclassification table (old value 2.2436 – 5.1605, new value 2)then click the Delete Entries button to the right. That row is removedfrom the reclassification table.

Repeat theabove procedure until there are just 3 entries in the reclassificationtable (not including the row for NoData NoData). When there are just 3entries click in first value under old values and change the range from0 – 2.2436 to 0 – 7.5 (note: it is critical that there is a spacebetween the hyphen and each of the range values). Change the othervalues to match the slope reclassification table listed above. Thenclick the OK button.

An alternate method tomodify the reclassification table is by clicking on the Classify…button on the Reclassify window. On the Classification window changethe Method from Manual to Equal Interval, then the Classes: value from10 to 3, then type the values 7.5, 15 and 60 as the 3 values in theBreak Values table to the right of the window.

Once you have reclassified the slope values a new layer called Reclassof Slope is added t the map. This is a raster data set similar to theslope layer but the values for this layer can only be 1, 2, or 3.

Step 4: Make Slope Reclassification a Permanent Data Set
Follow the procedure used in the last exercise to save the Reclass ofSlope layer as a permanent layer (save it in the Rasters folder withthe name SlopeClass).

Step 5: Relabel Slope Classification Layer
The previous slope reclassification procedure has produced a usefullayer but the default labels are somewhat hard to understand.

Wewill relabel the laye to make it more legible to the casual reader.First rename the Reclass of Slope layer in the Table of Contents toread Slope Class. Next bring up the layer’s property window and fromthe symbology tab change the labels from 1, 2, 3 to Flat (under 7.5%),Moderate (7.5-15%), Steep (over 15%). Feel free to change the slopeclass colors as well if you’d like.

Thisprocedure doesn’t do anything to modify the underlying data but it doesmake our map document easier for anyone to read and understand.

Step 6: Reclassify Distance to Water Values
Follow the previous steps to modify the distance to water layer to the following distance classes:
Distance Distance Class Distance Label
0 - 750 1 Close (under 750 m.)
750 - 2000 2 Moderate (750 m - 2 km)
2000 - 10000 3 Far (over 2 km.)

Make the layer a permanent data set in the rasters folder called H2ODistClass.

Relabel the layer to be Distance to Water Class, and change the class labels to match the entries listed in the table above.

Step 7: Agricultural Potential
An important factor in the daily life of agriculturalists is theagricultural productivity of the land they farm. Add the layerAg_Potential (in the E:\GIS_In_Archaeology\Data\Mexico folder) to themap. This is a polygon vector data set classifying the land into it’ssuitability for agriculture. In the attribute table there is a fieldcalled LType (Land Type) which classifies the land from 1 to 9 (1 isthe most suitable for agriculture, 8 the least suitable, and 9 is forwater).

Step 8: Vector to Raster Conversion
In order to summarize this data set along with the slope and distanceto water variables it is necessary to convert from a vector to a rasterdata set.
Click the down arrow next to the Spatial Analyst entry in the SpatialAnalyst Toolbox. Select Convert, Features to Raster from the drop downmenu. In the Features to Raster window set the following parametersInput features: Ag_Potential, Field: LType, Output cell size: 60, andOutput Raster: E:\GIS_In_Archaeology\Data\Mexico\Rasters\AgLands

Step 9: Agricultural Lands vs. Agricultural Productivity
Currently the agricultural lands are classified into 8 groups (pluslakes) for their agricultural suitability. These classes are arbitraryclasses and don’t necessarily reflect the agricultural productivity ofthe land. If we used the land classes as they stand we would basicallybe saying that type 1 lands are twice as productive as type 2 lands,three times as productive as type 3 lands, four times as productive astype 4 lands, etc. A study of the area indicates that this is not thecase and a more suitable agricultural productivity index would be:
Land Class Productivity Index Description
1 100 Most Productive
2 90 Highly Productive
3 70 Mod-High Productivity
4 60 Low-Mod Productivity
5 40 Low Productivity
6 40 Low Productivity
7 20 Least Productive
8 20 Least Productive
9 0 Lake

Use the previous techniques to create a Productivity Index using theabove values. Save this as a permanent data set in the Rasters foldercalled AgLandIndex.

Step 10: Local Soils vs. Agricultural Productivity
This last procedure created a 60 meter raster data set of agriculturallands indexed for productivity. That’s to say we classified each 60meter square for the agricultural suitability of the land within that60 meter square. From an agriculturalists perspective, however, this isnot necessarily the most appropriate measure of the agriculturalproductivity of an area. It is most unlikely that an agriculturalistswould limit their selection of agricultural soils to just the 60 metersquare surrounding their settlement. Various studies ofagriculturalists indicate that they are regularly willing to traveldistances of 1 km, 2 km, and even more to farm suitable soils.
Click the down arrow next to the Spatial Analyst entry in the SpatialAnalyst Toolbox. Select Neighborhood Statistics from the drop downmenu. In the Neighborhood statistics window alter the parameters tomatch the ones below. Modify the output raster data set to beE:\GIS_In_Archaeology\Data\Mexico\Rasters\Catchment1Km.

If you set the parameters correctly you will get a data set called Catchment1Km with values ranging from 0 to 79,700.

Step 11: Questions to Ponder
What does this data set represent?
Why did we use Sum as the Statistic type?
Why did we use a Circle Neighborhood
What does a Neighborhood setting of Radius: 1000, Units Map mean?

Step 12: Save Map and Exit
We will be using this map in a future homework exercise so make sure you save you map before exiting.

Georeferencing Scanned Maps

In this exercise we will learn how to take in a scanned paper map,bring it into ArcMap, and place it a geographic coordinate system sothat we can use it for digitizing data into ArcGIS

Step 13: Create a New Map Document
If you have not already saved your map from the previous exercise, doso now. Next start a new ArcMap map document project. Add theshapefiles Countries and States to your map

Step 14: Download Exercise Data
If you haven’t already done so Log on to Angel and download the fileLab_07.zip. Unzip the data files on to your V: drive. This should putthe data in a folder called Anth497G on your V-drive. If the unzipprocess asks you if you want to overwrite any existing data, respond Yes

This process should have save a new scanned map image calledCultures.tif to the V:\Anth497G\Lab_Data\Scans folder. This is a simpleblack and white map outlining some of the major archaeological cultureareas of Mesoamerica

Step 15: Load Georeferencing Toolbar
The process of putting an image into geographic coordinate space isknown as georeferencing. To perform this task in ArcMap we need to usetools that are available in the Georeferencing toolbar. From the Viewmenu go to Toolbars and check the entry for Georeferencing. This willmake the toolbar available for use:

Step 16: Add Scanned Image to Map
Add the scanned image Cultures.tif to your map document. When you dothis you will probably receive a message saying that one or more layersis missing spatial reference information. This is because the scannedimage is not associated with any geographic coordinate system. Clickthe OK button
Modify the layer to make Cutlrues.tif the top layer in the table ofcontents. Even though it is currently the top layer it will not appearon your map because it is not yet in the geographic coordinate system.
Use the zoom and pan tools so that your map is currently centered onthe countries of Mexico, Guatemala, Belize, Honduras, El Salvador andNicaragua.

Step 17: Bring Scanned Image into View
Click the down arrow next to the Georeferencing entry in theGeoreferencing Toolbox. Select Fit to Display from the drop down menu.This process fits the scanned image within the current map zoom extents– if you were zoomed to the proper scale it will now fit close to whereit belongs. Turn the cultures.tif layer on and off to view it’srelationship to the other layers.

Step 18: Assigning Control Points with the Mouse.
To bring the map into it’s proper geographic space we go through aprocess of assigning control points which mark the correspondencebetween coordinates on the scanned image to those on the geographicallypositioned layers.
On the scanned map there is a small island located above the text forMaya Lowlands. This corresponds to the island that you can see off theYucatan peninsula on the Countries layer. Zoom in to a scale where youcan see the island on the scanned image when it is turned on and on thecountries layer when the scanned image is turned off.
. What we need to do is select a point in the From Layer (the scannedimage) and then select a corresponding point in the To Layer (thecountries layer). Make sure the cultures.tif layer is on and visible,then select the Add Control Points tool in the georeferencing toolbox.Your cursor now turns into a cross-hair design, click a point more orless in the center of the island on the scanned image, you will now seea rubber-band line as you move away from that point. Turn off thecultures layer and then select a point in the center of the island onthe countries layer. If you turn the cultures layer back on you willsee that it has been “dragged” so that the two points you selecteddirectly overlay.

Step 19: Assigning Control Points with known X, Y coordinates
Using the mouse to assign the correspondence between two points workswell for points that we can see visually but which don’t have welldefined coordinates associated with them. If we know the actualgeographic coordinates that a point should have then it is better tokey in those values. On the scanned image there is a well definedcorner point where the border between Texas and Mexico. This pointshould have a geographic coordinate of -97.14 degrees latitude, 25.97degrees longitude.

Turn the cultures layer on and Zoom to a scale where you are zoomed inclosely on this point. Again select the Add Control Points tool andclick on this point. Instead of left-clicking on another point (as wedid above) right click the mouse and select Input X and Y from thepop-up menu.

In the Enter Coordinates window enter the values X: -97.14 and Y: 25.97

The scanned map is now in a somewhat better location with regards to the countries layer.

Step 20: Refining the Georeferencing
Using the techniques listed above enter more control points to furtherrefine the fit of the map. Make sure that you always select a pointfirst on the scanned layer and then on the countries layer. Try to geta selection of points from various parts of the scanned image.

Step 21: Deleting Controls Points
If you make a mistake during the georeferencing process you can eitheruse the Undo tool to undo the last point. Alternately you can view thepoints you’ve assigned by using the View Link Table tool.

This will bring up the Link Table which will show all the points youselected. You can remove a link by highlighting it and then pressingthe Delete key.

Step 22: Saving the Link Table
Whenare satisfied with points you have selected you should save away thelink table information. Open the Link Table as outlined above and thenclick the Save button. Save the link table into the Scan folder withthe file name: Cultures.txt. This way it is possible to revisit yourgeoreferencing procedure in the future.

Step 23: Saving the Georeferencing Image
Also once you have complete the process you can save a copy of the mapsaved in the current geographic space. Click the down arrow next to theGeoreferencing entry in the Georeferencing Toolbox. Select Rectify fromthe drop down menu. Save the Output Raster as RectifyCultures.tif inthe E:\GIS_In_Archaeology\Data\Scans\ folder. Click OK to accept therest of the default values and save the georeferenced image. We willuse this in a future exercise.

 

Step 24: Save Map and Exit
Save the Map document and Exit.

from:http://www.indiana.edu/~arch/saa/matrix/agis/agis_lab_7.htm