Latest Contributions by CaiLadd

Dear all,    I'm hoping you can advise on what may be a very simple problem. Here's the scenario: I have several maps of an estuary, each separated by ten years from the last. On each map are two variables: position of salt marsh edge and position of the main water channel along the estuary (currently, the water channel is a polyline, and the marsh is actually in the form of a polygon, mapping its entire area, not just the edge). I want to know if there's a relationship between change in channel position and change of the marsh edge over time. My H1 is that "the marsh edge moves away from the tidal channel at a given threshold proximity" (because the closer a water channel is to the marsh edge, the more erosion there is, although the channel has to be close enough to start the erosion process, hence the threshold proximity). This simple model is analogous to that of a magnet - two magnets with opposite poles facing each other, lie on a table. As you start to move magnet A closer to magnet B, Magnet B does not start moving until Magnet A is close enough to overcome the friction between magnet B and the table. Magnet A is the water channel and magnet B is the salt marsh. So, my problem. How would I demonstrate a statistical relationship between channel position and marsh edge erosion? Demonstrating it graphically is also a challenge I have! Thank you in advance for any advice you can offer. All the best,    Cai ... View more

I'm working on digitising aerial images of saltmarshes onto ArcGIS, so that I can measure change in extent over time. To do this, I had a georeferenced image loaded on Adobe Photoshop Elements (figure 1). There, I extracted the 'saltmarsh', and subsequently re-georeferenced that image back into ArcGIS 9, but this time with only the parts that I'm interested in (figure 2). Now, I want to convert all the greenish stuff into a shapefile. What is the best way to do this? I didn't want to create a new polygon by hand because as you can see, the structure is rather complex and it would be time consuming to draw it accurately (I have many more images to process after this). Any ideas? Your help would be really appreciated? Thanks,    C [ATTACH=CONFIG]29530[/ATTACH] Figure 1: Saltmarsh image. [ATTACH=CONFIG]29531[/ATTACH] Figure 2: Saltmarsh aera removed from background - I now want to convert this section of image into a shapefile. How do I do this? ... View more