# making a Drainage density map-square modules method!

5 replies to this topic

### #1 Covasnianu Adrian Posted 21 December 2010 - 04:30 PM

Contributor

• Validated Member
• 48 posts
• Gender:Male
• Location:Iasi
• Romania

Hello!

I'm trying to create a drainage/fragmentation density map using the square modules method (cartograms).

Such as this map: drainage map

In ESRI ArcMap I've followed the steps of digitizing the rivers, calculated the length and after that with Line Density from Arctoolbox the drainage density was generated.

Next, I want to calculate on grids of 1 square km the line density of the rivers.

In the end, the map will look like a "puzzle", but, I don't know how to finish the map.

Using ArcView 3.X there is a script called FeatureDensity which is the solution.

But I want to use an equivalent of the current script or any other solution (proprietary or open-source software) for the drainage density map.

Sincerely,
GIS user

PhD geographer
CUGUAT-TIGRIS Research Center
University Al.I.Cuza Iaşi
Faculty of Geography & Geology

### #2 SaultDon Posted 21 December 2010 - 07:53 PM

SaultDon

Master Contributor

• Validated Member
• 153 posts
• Gender:Male
• Location:BC
• Interests:Environmental/Wildlife GIS, Aboriginal Land Use and Occupancy

Next, I want to calculate on grids of 1 square km the line density of the rivers.

But I want to use an equivalent of the current script or any other solution (proprietary or open-source software) for the drainage density map.

A couple of ways you can do this, because I am pretty sure your line density is the sum of the river(s) length that fall within that particular cell (the same values that are represented in the example map you provided and what the example tool was going to do) so this is what I propose. Its a vector based analysis.

ie,)
Cell,Length Total
A,175.22
B,222.43
C,41.2
etc...

And then, when those summed river lengths are recorded as an attribute to the sqkm grid, they can be drawn using your own distribution through the Symbology tab of that layers properties dialog (right click, properties - or double click).

Here's what you can do to.

Do you have your grid already? If not, a couple of ways to make one, here is one example:
-create a grid using the Create Constant Raster tool (this raster will cover your entire extent, which may be a mask set by a polygon in the environment settings)
-convert the output raster to a polygon using Raster to Polygon (use no_simplify)
-if your new polygon grid needs to be simplified to your area of interest, like an irregularly shaped polygon, then you will need the next step.

-use Select by Location to grab the polygon grids that intersect your area of interest layer, like a watershed
-with this selection active (the polygon grids that did intersect will be highlighted), right click that layer in the table of contents, go to Data -> Export Data. Be sure that the features you are exporting are the Selected Features and that the proper projection is being applied from either the data frame or the source data.

-with the new grid polygon, open the attribute table because we need to assign a unique id.
-add a new field to this attribute table, make it text and the default 50 characters should do fine
-right click this text fields header and click Field Calculator. Use the following expression:
`"abc_" & [OID] + 1`
That OID field is a field that would of been automatically generated as part of the shapefile. It should be numbered 0-99 or however many records you have. If not, it could be called something similar.
-delete any excess fields, like "Value" if it is there so that your new text field is the only one there
There will be fields you cannot delete, they are usually denoted with an asterisk *

-now there is a UID in that polygon grid (that's also been simplified to your area of interest)
-use the Intersect tool with the rivers and the polygon grid as the inputs, the default parameters made by the tool should be ok, but go over them if you are not familiar with them, or check out the tools help description if you think they need to be changed
-once the tool has ran, it will output a line feature class that duplicates your rivers, but it will have an attribute attached to them now that is the same name as the text field you created in the polygon grid, called something like "UID"
-right click this field in the new river lines attribute table, and Summarize, also placing a checkmark beside SUM underneath your RiverLength field, hit OK.
-add that resulting table to the map, and Join it to your polygon grid based on the matching column in both of them, "UID"

-that polygon grid can now be symbolized by RiverLength using any distribution you like using Quantities (found on the left hand side panel of the Symbology tab)

I hope that's what you were thinking. Let me know, of course, if something doesn't work or make any sense. I hope I never missed a step because I am writing this on the go.

### #3 Covasnianu Adrian Posted 22 December 2010 - 01:02 PM

Contributor

• Validated Member
• 48 posts
• Gender:Male
• Location:Iasi
• Romania

Hello,

I've created a grid with cell size of 1.000 meters.
After that, I've created a field and populated with unique values (more than 800).

I'm stuck in intersect tool....

I'm inserting the layer with rivers (polyline features) and the grid layer (polygon features). In Intersect tool I've selected all in JoinAttributes and Output type INPUT.
The resultated shp is a polyline ....etc. etc.

Finally, after some research and asking a friend, using kernel density from toolbox, the result was obtained.

Thanks!
GIS user

PhD geographer
CUGUAT-TIGRIS Research Center
University Al.I.Cuza Iaşi
Faculty of Geography & Geology

### #4 SaultDon Posted 22 December 2010 - 03:39 PM

SaultDon

Master Contributor

• Validated Member
• 153 posts
• Gender:Male
• Location:BC
• Interests:Environmental/Wildlife GIS, Aboriginal Land Use and Occupancy

Glad you discovered the kernel density tool.

For future reference, because if you are like me and don't always have access to spatial analyst,

here is the method i've described in detail as a Word DOC.

link to Google Docs PDF: Creating a Chloropleth Map without Spatial Analyst in ArcGIS 9.3.1

### #5 Covasnianu Adrian Posted 22 December 2010 - 03:47 PM

Contributor

• Validated Member
• 48 posts
• Gender:Male
• Location:Iasi
• Romania

Thanks a lot for the pdf.It's very intuitive.

Sincerely,
GIS user

PhD geographer
CUGUAT-TIGRIS Research Center
University Al.I.Cuza Iaşi
Faculty of Geography & Geology

### #6 MapMedia Posted 22 December 2010 - 11:19 PM

MapMedia

Hall of Fame

• Validated Member
• 1,029 posts
• Gender:Male
• Location:Davis, California
• United States

Create a grid, as desired using a mesh script. Then intersect hydrology with grids. Summarize total hydro lines within each cell. Divide by square km area of grid cell and you have a line density value for each cell.

#### 0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->