Double meaning of relief

Solution 1:

You’ve already made the right choice, because relief is the precise and correct word for what you want. It is pronounced the same way that its homograph is, the one you mentioned being about feelings and such.

The OED lists these two words completely separately. In fact, it has three different nouns here, although the first is obsolete as of the 16th century or so. These words came into all the European languages around the same time, because the literate were frequently literate in many languages and freely borrowed from one another.

1. † noun¹: c. 1225–1589
   Several related meanings connected to scraps left-overs, mostly those from a meal. No longer current. Their etymological notes mention:

   Compare Old Occitan releu, Catalan relleu (13th cent. as †releu; now regional), Spanish relieve (1251; chiefly in plural relieves; now archaic), Italian rilievo (a1288; now archaic or literary; also as †rilevo, †relievo), all originally and chiefly in sense 2, and Middle Dutch relief, relif remainder, (specifically) remains of food left after a meal (both late 13th cent.). Although in early use the English word often translates classical Latin reliquiae (plural) (see reliquiae n.), neither relief n.¹ nor its French etymon are etymologically related to the Latin plural noun.

2. noun²: a. 1325–present
   This is the more common of the two current meanings. The OED places it in the same frequency band as it places dog, horse, ship, machine, mile, assessment, army, career, which means that it occurs between 10 and 100 times per million words in typical modern English usage. They identify its etymons as (Old) French releef, relief; the verb relieve, and Latin relevium. Specifically they mention:
   

   Probably partly < Anglo-Norman releef, relef, releff, relif, Anglo-Norman and Middle French relief (French (now hist.) relief) payment made to the overlord by the heir of a feudal tenant on taking up possession of the vacant estate (1215 or earlier in Anglo-Norman), formal acknowledgement of feudal tenure made by a vassal to a lord (13th cent. in Old French), alleviation (late 14th cent. or earlier in Anglo-Norman; < relever relieve v.), and partly (especially in later use) < relieve v. In sense 1a perhaps also partly < post-classical Latin relevium relevy n.1; compare Middle Dutch relief, relif, in same sense (end of the 13th cent.; < Old French; Dutch (now hist.) relief), and also post-classical Latin relevamentum (see relievement n.), relevatio (see relevation n.).

3. noun³: 1606–present
   This is pronounced the same way as the previous one is, rhyming with belief. The OED places it in their frequency band 5, unlike the previous word which they place in 6. That means it occurs from 1 to 10 times per million words in ordinary English. They mention:

   The shift away from the everyday language found in bands 8-6 is apparent in nouns (e.g. surveillance, assimilation, tumult, penchant, paraphrase, admixture)

   So it isn't super rare in any way; those are normal words. They identify its etymons as Italian rilievo, relevo, relievo and French relief, and they suggest that one

   Compare Spanish relievo (late 16th cent.; < Italian or French), Dutch reliëf (1659 as relief; < French), early modern German relievo (c1650; < Italian), German Relief (18th cent.; < French).

As I said, this is the right word to use here. Let me cherry-pick of few of the senses they cite it gets used in today, along with their most recent of many, many citations for each of these I’ve selected.

1. a. Moulding, carving, stamping, etc., in which the design stands out from a plane surface so as to have a natural and solid appearance. Also: work done in this way; the part which so projects. Sometimes with modifying word specifying the degree of projection: see high relief n. 1, low relief n., bas-relief n.

   • 2008 Edmond (Oklahoma) Sun (Nexis) 4 Oct.
     The heaviest object, a marble sarcophagus,..is heavily decorated with carved relief.

2. c. figurative and in figurative context. Vividness, distinctness, or prominence due to contrast or method of presentation. Frequently as to throw (or bring, etc.) into relief.

   • 1991 K. Jones Learning not to be First ix. 103
     Lizzie became pregnant, and the sickly young woman's fecundity threw Christina's own barrenness into stark relief.

3. b. Physical Geography. The manner or degree of variation in elevation of a part of the surface of the earth (or other planetary body).

   • 1990 Technol. Rev. Nov. 10/1
     Some scientists have said the sharp relief of many mountains suggests these areas have recently grown.

They list many compounds in which this version of relief is used, including: in relief, relief block, relief carving, relief construction, relief decoration, relief map, relief panel, relief plate, relief polish, relief polishing, relief portion, relief print, relief printing, relief process, relief stamp, relief stamper, and relief tablet. In my own personal experience, relief map is the one of those that I come across the most often.

So this is a perfectly normal word, and I would not hesitate to use it in your technical context.

Solution 2:

Relief is OK if there's sufficient context, but for just a few more characters you could just write out what you mean:

...shows more variation in height.

...shows a larger range of elevations.

...shows more extreme values.

...shows a wider range of values.

...shows more contrast.

Etc. Mix and match to your liking, as pertains to whatever you're trying to show with your map.