Assistance with interpolation and boundary setting

[KevinDaly]

Hi all, I apologize if this message was posted in the wrong board or if it is too specific - just a new user of ArGis feeling quite overwhelmed with what I am trying to do.

Basically I would like to do the following: perform interpolation of values that are scattered across Europe (mainland and islands i.e. Ireland, Iceland), Africa (mainland and islands i.e. Morocco) and Africa. I would like the interpolation to reach only the continental boundaries (i.e. stop at the oceans), and also for interpolation to "go past" the exterior points (i.e. I have data points in the centre of some islands/countries, but I would like the interpolated figures to exceed those and reach the land edge - and I don't have values "further out" from these points).

I have attached an image of something similar to what I would like to achieve - in my case, I want a much broader geographic area.

I am very unfamiliar with this software and file formats. I had hoped that I could have done one of two things to achieve the plot I wanted:

1) Interpolate only to the boundaries of the continents of interest, or

2) Interpolate across the boundaries, but in some way mask the oceans

I had thought the second could be achieved using something like Inkscape, but when I tested a .svg file created from ArcGis, the entire image was in a single layer i.e. I could not remove the oceans. 

I would greatly appreciate any help with this. I have figured out how to upload my csv and run interpolation on the points, but the interpolation stops at the boundries of my data (i.e. does not interpolate past the most extreme points), I cannot figure out how to either set interpolation to go as far the continent boundaries or how to separate oceans and landmass, or even colour them different (preferably grey).

[DanPatterson_Retired]

you can make an ocean mask by intersecting a large polygon with your continental areas.  Dump the land, leaving the ocean/water mask.  Do your interpolation, noting the cell size and extent of the output.  Convert your ocean/water to a raster using the same cell size and extent, assign a value of 0 to the water.  You can then simply mask the map by putting the ocean layer on top (assuming nodata cells are transparent.  If you want to combine the rasters, then you can use the 'con' statement  details depend on your inputs names, but Con('water' == 0, 'water', 'your_other_raster') 

[KevinDaly]

Thanks Dan. Sorry for asking you to spell this out a bit more but I really

am overwhelmed by this software. Though I understand the general gist of

what is recommended, it's led to some more/unanswered questions:

1) Is there a way to interpolate past the boundaries of my data?

2) "You can make an ocean mask by intersecting a large polygon with your

continental areas. Dump the land, leaving the ocean/water mask " - is what

is meant manually create a polygon that overlaps with the ocean, then

intersect the map and the polygon mask to leave only an ocean mask

(polygon)?

3) How do I "note the cell size and extent of the output"?

4) How do I "convert your ocean/water to a raster using the same cell size

and extent, assign a value of 0 to the water"? What value is being assign

0? The interpolated value? How do I assign this specifically to the water -

is this during the raster conversion step?

5) Is the final step to just move the raster ocean layer (with value zero)

to the top, obscuring the the ocean's original interpolate value?

6) "f you want to combine the rasters" - which rasters do you mean?

Really appreciate your help with this, thanks!