Let $M$ be a connected, non-compact $m$-dimensional Riemannian
manifold. In this paper we consider smooth maps $\varphi: M
\rightarrow \mathbb{R}^n$ with images inside a non-degenerate
cone. Under quite general assumptions on $M$, we provide a lower
bound for the width of the cone in terms of the energy and the
tension of $\varphi$ and a metric parameter. As a side product, we
recover some well known results concerning harmonic maps, minimal
immersions and Kähler submanifolds. In case $\varphi$ is an
isometric immersion, we also show that, if $M$ is sufficiently
well-behaved and has non-positive sectional curvature,
$\varphi(M)$ cannot be contained into a non-degenerate cone of
$\mathbb{R}^{2m-1}$.