Q: Retrieve LINK_ATTRIBUTE_FC1..5 based on LINK_ID Assume I have a LINK_ID which I got using the LINK_FC5 layer with search/proximity resource described here.
Note that the search/proximity resource doesn't allow non-geometric layers such as LINK_ATTRIBUTE_FC5 to be specified. 

Errorcode: 400, message: Provided layer does not contain geometries.

The documentation suggests using tile resource for getting the non-geometric layers, but that seems quite inefficient. Within one tile there are many LINK_IDs. Hard for me to believe there is no better way to do this. Hence the question:
What is a efficient way to retrieve all attributes from the LINK_ATTRIBUTE_FC5 layer using the LINK_ID?

A: You need to club to APIs to get the desired attributes for link IDs. So a tile comprises of multiple layers, Each layer contains multiple link IDs. this requires to make association between these resources. You can also refer to example : https://tcs.ext.here.com/examples/v3/pde_get_any_link_info
First API is : 
https://s.fleet.ls.hereapi.com/1/index.json?layer=ROAD_GEOM_FCn&attributes=LINK_ID&values=548294575,833539855,550088940,930893121&apiKey=xxx 
The response will be like : 
"Layers": [
        {
            "layer": "ROAD_GEOM_FC5",
            "level": 13,
            "tileXYs": [
                {
                    "x": 8580,
                    "y": 6376
                }
            ]
        },
        {
            "layer": "ROAD_GEOM_FC1",
            "level": 9,
            "tileXYs": [
                {
                    "x": 534,
                    "y": 397
                },
                {
                    "x": 536,
                    "y": 398
                }
            ]
        }
From here you will get level, tile x,y and layer, 
2nd API will be : 
https://s.fleet.ls.hereapi.com/1/tiles.json?apiKey=xx&tilexy=536,398&levels=13&layers=LINK_ATTRIBUTE_FC5
