hi... i'm a software dev who's interested in creating dynamic SVG's to overlay over a static map, 

i thought i could use inkscape to make it manually to see how to code looks like in xml 

is saw someone allready doing something very similar and was wonderign how one can do that. 

i'm assuming some form of mesh gradients are involved..

https://community.qlik.com/t5/QlikView-App-Dev/SVG-HEATMAP-INDUSTRIAL-PLANT/m-p/1217371

Hi and welcome. When I click on the link you shared the site asks me to register for an account there. Do you have an actual heatmap example image that can be shared? I am cautious about just willy nilly registering to a site I am not familiar with.

I don´t have to sign in, rejected cookies and have access right away.

I managed to gain access and view the image. This will be probably done using mesh gradients as you suggested. At the site you stated you wanted to know if there was an extension available to achieve this. I am not aware of any such extension. Perhaps Polygon or others.can step in and offer better ideas.

i'm not the auther of that message, i simply used their image as an example, :) so i'm not after any extension.

what i really wanna know is how to create this via an svg api library , but i'm not familiar with SVG, so the first thing i need to know is how to create this manually, look at the SVG code produced and figure out how to do it automatically,. 

so i needed to know the proper terminology and steps to do that. 

Watch:

https://youtube.com/watch?v=zE0GbVLIqmA&feature=shares

https://youtube.com/watch?v=2G5hfRhw6gU&feature=shares

https://youtube.com/watch?v=YdqndZ6T3MA&feature=shares

so i'm trying to figure out in general what is a gradient mesh...

it's basicaly a grid where you can define colors to each intersection of edges of the mesh , including  the center.

those colors spread from the vertiex they were defined on they would gradualy face into colors that were defined around the edges. 

See:

https://inkscape-manuals.readthedocs.io/en/latest/creating-a-mesh-gradient.html

https://markoze.com/tutorial/awesome-gradients-inkscape/

https://designbundles.net/design-school/how-to-use-gradient-mesh-in-inkscape

https://www.chrishilbig.com/mesh-gradients/

Here's my attempt. Use the node tool to adjust the shape and position of each heat source then hide the "Heat Sources" layer.

The layer "Heat Map" uses [Path > Path Effects...] [Clone] and [Offset] to reproduce the colour bands. A clipping path restricts the colouring to an area of interest. Blurring the group softens the colour boundaries. [Blend Mode: Darken] is applied to the layer so that the monochrome floor plan can be seen through the colours.

This is visually similar to your heat map but it doesn't accurately model the transitions from hot to cold. You can adjust these by changing blurs and offset distances. Instead of blurring the grouped colours, you could blur each element of the group individually.