HQ threat decay description

[dcdenu4]

Adding clarity about how threats are decayed when using exponential decay method. This will better line up with InVEST HQ changes that will be released in 3.13.0 where we switch using convolutions to decay threats and use euclidean distance transforms.

Also adding in a new updated figure to demonstrate exponential decay.

@lmandle, @newtpatrol, @jade-md I'm adding you all as reviewers, but it is kind of a pain to review these updates without being able to see the RST compiled nicely. So, feel free to review here OR I can share a built version for viewing and we can edit in a google doc or something.

[dcdenu4]

Hey @lmandle, I made those edits you suggested. I also updated the figure to show that it drives to 0 at max distance and added more points for a continuous look.

For the Figure caption, I've left it unchanged with:

Figure 1. An example of the relationship between the distance-decay rate of a threat and the maximum effective distance of a threat.

So, if that figure caption seems okay and the graph looks good, then you can "Approve" and if you'd like, you can Merge by clicking "Merge pull request" -> "Confirm merge".

In case you're curious, at the top this PR shows we're committing into natcap:release/3.13.0. Normally we'd merge right into the main branch, but since these changes won't be "live" until the 3.13.0 InVEST release we create a Users Guide release branch to "store" them under. Otherwise the changes would show up in the UG now and be out of sink with the current InVEST release.

I also wanted to note, in case you didn't know, that when reviewing RST files you can select to view them as rendered by clicking the little page icon (highlighted in yellow in the example below)

[newtpatrol]

I just took a look at Figure 1, and wonder if I might request some improvements to it. Perhaps it will be visually larger in the final release, but as it is, I can barely read any of the text. It would also be useful to have a legend title for what the 1km...5km lines mean. It's also kinda hard to tell some of those color lightness gradations apart, so maybe better to use different colors, and/or label each one somehow (or some other way of differentiating). If all of this makes you say "how about you do that yourself?" I'd be happy to take a shot if you provide whatever source you're working with.

[dcdenu4]

@newtpatrol, since you've kindly offered 😉 , here is the source for the figure! This source will also be committed into the repository, so after you've edited and made a new figure, just upload it back here and I can upload the new figure and source to this PR. I've been working from an Excel file, for reasons, but hopefully this isn't too much a pain to edit... I'm no Excel graph pro, so I was making custom data entries and such to get what I wanted... Good luck!

HQ-decay-functions-chart.xlsx

[dcdenu4]

Hey @newtpatrol, I took a stab at updating the figure. I changed the color scheme, added a legend title, renamed the x-axis, and added a figure title. I made the fonts bigger everywhere. Let me know what you think.

Habitat Quality — InVEST documentation.pdf

[dcdenu4]

Okay, I chatted with Stacie and we are going to go with the updated figure I made. We can always change it at any time.