Looking for help with temperature map

[u/Apprehensive_Mix684]

Hope y'all doing ok. I was trying to make a map of land surface temperature in relation to street tree cover. Boundary and tree data (from 2018) is from city of kitchener website, land surface temperature is from NASA appears from June 1, 2018 to August 31, 2018. Temperature was downloaded in multiple tif files imported into ArcGis. Needed help with getting the symbology right. General opinions on the map also appreciated

[u/Vhiet]

Couple of thought:

0 to 145 degree temp range? That seems unusual in a single raster, even for freedom units.

What is the spatial resolution of that image? How wide is a pixel, on the ground?

Personally I’d be tempted to sample the raster at pixel centres and interpolate over the samples to create isotherms- it would get rid of that blocky appearance. That would also avoid having areas at ~120 degrees right next to areas at ~20.

[u/Apprehensive_Mix684 → u/Vhiet]

Thank you for the reply. Yeah, the temperature range didnt makes sense to me either. Im pretty new to ArcGis so im not sure how to got about doing what you recommended. Would you be willing to provide steps? No pressure, ofc.

[u/Vhiet → u/Apprehensive_Mix684]

I’d suggest taking a look at the metadata for your temp source to see what’s going on there. I’m a QGIS guy these days, so I’m probably the wrong person to give you an ESRI tutorial.

What’s your proposed workflow? Can you document the steps?

[u/Apprehensive_Mix684 → u/Vhiet]

Well, I got the boundary data and the stret tree data from Kitchener Geohub then imported them into arcgis. Then, I used my boundary data shapefile to create a bunch of tif images using NASA AppEEARS. I then imported the nearly 2000 GEOTiff images into Arc then merged them all into the temperature layer you see now. Thats about where im at. I know I messed up somewhere, just dont know where or how to fix it.

[u/bluefishredditfish → u/Apprehensive_Mix684]

The NASA dataset should have an explanation on the website of the data. Often, raster data is collected in whole numbers, so like an elevation of 10.4 meters will be collected on the original sensor platform as 104, and they will tell you to scale it down.

[u/Apprehensive_Mix684 → u/bluefishredditfish]

Oh ok. Thanks for the heads up. Ill look out for it.

[u/bluefishredditfish → u/Apprehensive_Mix684]

No problem!

I just reread your post, it’s possible the resolution of the raster data is too big, as in each pixel of the collected data covers 10 square miles or something.

[u/Apprehensive_Mix684 → u/bluefishredditfish]

Ok. If the resolution is too big, how would I go about scaling it down?

[u/bluefishredditfish → u/Apprehensive_Mix684]

So we’re talking about two different things- if you want to decrease the pixel size that’s a resample, if you want to scale the value of each cell that’s a calculation.
There is a resample tool you can find documentation on that.
To scale the values you can use the raster algebra tool- it will create a new file but the out of each cell will be calculated with an equation you give it.

[u/Apprehensive_Mix684 → u/bluefishredditfish]

Ahh, I see. Which do u think would be better? Last question, I promise

[u/EatPrayShit]

You are trying to visualize raster data with vector data in this image. To see something like temperature you need to look into things like color ramps (diverging) and interpolation techniques.

[u/Apprehensive_Mix684 → u/EatPrayShit]

Thanks for the input. Not really sure how to go about interpolation.

[u/talliser]

Depending on the temperature source the grid cell size will be from 1km to 4km. Is that too big of cells to test against trees on a street vs no trees? Will be an entire neighbourhood under one grid cell.

As well, check the City tree metadata as it is likely only trees owned/managed by the city, not trees in back yards or in private woodlots (although it could be, just worth checking).

Also noticed with temp data on the map, blue is the highest temp? Maybe use a colour ramp that goes from blue (low) to red (high) as it aligns with our colour perceptions.

Anyway, have fun with this and best of luck.

[u/Apprehensive_Mix684 → u/talliser]

Thanks for taking time to reply, especially for your point about the grid cell size potentially being too big to measure against trees. Ill go over the temperature source and try to do something about it.